Be sure to let him see you place food in the enclosure with the tongs. Give him time to get used to seeing your hand. He will probably begin to anticipate you placing the food and put himself in a spot to meet you.
Also let him see you harmlessly servicing the enclosure, tidying up and changing water. Move slowly and deliberately, they are programmed to react to quick motions,
Yes, they can be seasonal, but that very much depends on how he is kept. We have hot summers here (102F/39C today) and cold winters (average daily temp @32F/0C with frequent dips into the teens/<-7C). We keep the house at 73F/23C in winter and 80F/27C in summer.
I keep my Ackies with lights on a timer (12 hrs/day) and in enclosures that resist temperature extremes, in a conditioned space. I have a Deep Heat Projector and a halogen lamp shining on a flat rock big enough to bask on. The DHP remains on 24/7 to keep the enclosure warm, the halogen lamp goes with the timer to bump the basking heat and provide a bright spot during the day. Except the limited natural light that filters in through the curtained windows, which is a fraction of the intensity of their basking lamp and UV-B, their daily cycle is set by the timer and I don't think they know what time of year it is - they are active year-round.
It may still be a little soon to expect him to accept food from the tongs if that's how he behaves. How large are your tongs? A little one can be intimidated by hardware that is too bulky or bright.
What are you feeding him?
Mine get 95% whole prey (crickets, waxworms and superworms (when they get bigger)), with "treats". Treats are very small pieces of soft-scrambled egg (no cooking oils, just stirred & microwaved in a glass dish), lean meat like raw chicken breast, and fresh fish. You might try tempting him by laying a tiny piece of wetted chicken or fish (so it's not so sticky) where he'll see it quickly. I've also started them on forceps with cut up waxworms and sometimes have to touch the nose of the new babies to let them understand what it is.
The actual time varies with many factors, and also varies with your behavioral expectations. I don't think I can say it will take a certain number of days or weeks to reach a certain level.
Animals vary tremendously, even within a single species. I had one Beardie that was so acclimated to me touching and feeding him, he wouldn't eat unless I handed it to him. I had another adoption whose only desire was to kill me, in spite of how docile most are.
Building/maintaining trust is an ongoing process and there are several plateaus that are reached, but it really needs to be an ongoing thing. I reach in every morning and touch mine, lightly rubbing a head, chin or the side of their belly, gently lifting a dangling tail...brief non-threatening exposure/reinforcement.
Something not often mentioned is eye contact and avoidance. Try not to stare at your animal. To be stared upon by a binocular-vision (predatory) being is unsettling to many animals and especially birds. Use one eye at a time or turn your head off to the side as to not appear focused.
Being lower also helps avoid fear. Try not to tower over you Ackie. Although many of my babies were raised against common advice in open top aquariums, they got used to me coming in from above from the time they were hatched. In fact, I started working with mine when they were very young and they never really got a chance to learn to be afraid of me.
This is not always true of animals bought from others, and many breeders don't spend any real time with the babies. It DOES take a lot of time, but I felt that it was a big advantage to the final owner to receive an animal that was already well socialized. I realize the frustration of having an animal that is afraid of you and it can be stressful to both, especially an inexperienced owner.
Getting an Ackie used to seeing you in the enclosure is a big start and will go hand-in-hand with their acceptance of tong feeding. Let them see the tongs deliver the food. Tempt them by dangling a food item nearby, lightly drag it nearby to spread scent.
Once he trusts you enough to approach you for food, you can use food as a tool to gain compliance. Bait him up close to your other hand before releasing the tidbit, then work him onto your hand, making that the food bowl. I don't mean to tell you to starve your animal at all, but being a little hungry improves cooperation immensely, as does the desire for something special.
As he gets used to taking food from tongs, shorten your grip to get your fingers closer to him little by little. You will eventually be able to abandon the tongs, although every once in a while one of my adults might snag me with a tooth while enthusiastically accepting food. I think adult Ackies are about as a large a monitor I'd want to hand feed and even an Ackie can accidentally draw a few dots of blood if they are aggressive feeders.
It won't take long if you spend small blocks of time with him often. 5-10 minutes a few times a day would be ideal. I think it is important to spend a little bit of quality time, then withdraw on a positive note. As soon as he accepts something from your tongs, put the rest of his meal where he can get it and back out. That method seems much more productive than overloading the Ackie's tolerance and letting him terminate the session. If you wait until he goes in to leave, he will learn to go in so you will leave.
As he gets used to coming into your hand for food, you can touch him with a finger while he's there. I find they are most tolerant of being lightly touched on the flanks and underside of the tail early on and it sometimes takes time to permit head rubs.
Be careful, they can be extremely fast and if he rapidly climbs your arm and gets out, there is risk of injury from the fall and forcibly catching him will be terrifying. One escape can cost you weeks or months of trust if not handled correctly. If he does get out, try to trap him in a small box against the wall or throw a small towel over him as to keep your hand from being the "bad guy".
Early and often:
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Leaving my hand in his path:
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Avoiding me this pass:
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Success, if only for an instant:
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I bought this one as a young adult and he was extremely shy at first. He had never been handled and it took six months to get to this. Food (scrambled egg in this case) is a powerful tool.
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Patience pays off. This one looks forward to coming out and requires very little encouragement:
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