Taking thyroid meds at night fits in with the bodies natural rhythm.
Paul robinson recommends taking T3 specifically early in the morning before we wake up (around 4/5/6 am).
Dr John Lowe recommended we take all the T3 for the day at bedtime.
This is the principal behind why we should take thyroid meds at night, but not actually in the night just at bedtime.
TSH is highest by the end of the day. We are tired and go to bed. When we sleep the body repairs itself. So hormones have been used up during the day and are now lower. So for the thyroid TSH is high and when we nod off the body gets working and makes the T4 for the next day. This happens in the first part of the night. In the second half the body can see what thyroid has been made and goes about making a corresponding cortisol amount to match the next days interactions.
In a perfect world we make a good amount of thyroid and then cortisol and all is well for the next day. The body is not in a stressed state and has enough thyroid to power on through and cortisol to match this power.
If we are low in thyroid (when hypo) then not enough thyroid hormone is made for the next day. The cortisol amount is also lower. So we are running low the following day and have to rely on the adrenal system to help push us on. This is why we get adrenaline spikes and anxiety. Eventually the adrenals don't or cant act as back up and they really flat line. I think people like this end up absolutely knackered and in bed for a lot of the day.
So give thyroid hormones at night because these will also nurture the cortisol / thyroid relationship which is the key to good health.
Some people find they can't sleep as well if taken at night, but i would say stick with it and see how you get on over some weeks. I myself have no issues with falling asleep.