Fertilizer burn is almost instantaneous, like just one or two days tops. The leaves will turn yellow then brown on the leaf margins, not the leaf middles. It sounds like you are overdoing the fertilizer. Fertilizer accounts for only 3% of the nutrients plants need, the other 97% they make themselves through photosynthesis. If you fertilizer every other month with fertilizer mixed at half strength, during active growth, your plants would have more than enough. You aren't actually fertilizing the plant, you are bulking up the soil so the plants can use what they need and they really don't need very much.
Leaf yellowing could be caused by over or underwatering. Overwatered plant leaves go yellow because there is not enough oxygen in the soil for them to utilize iron and other trace minerals. Underwatered leaves turn yellow because the roots are compromised and can't support them.
The lights shouldn't be on for more than 14 hrs or so a day but I suspect you don't have strong enough lights. When the light is insufficient but causing the plants to stay overwarm, the plants will respond just as you described. They are growing desperately towards the light while the warmth stimulates excessive growth. That leads to another problem: Too many leaves for the compromised roots to support.
These are just guesses as you haven't provided photos of plants or lights or specs on the lights.
