Is this light burn?

Great work on this grow! I would not 100% say its light burn, It could be a bit of fading at the end of the plants life. It resembles the beginning of a lot of things like nitrogen, potassium and ca+mg issues. The lower leaves in your diary do look a bit hungry but the upper structure is looking on track for a 7-10 day harvest. In all honesty just leave it at this point don't worry to much about anything this close to harvest. It cant die that fast if you keep up your regular maintenance like you have been doing and simple watering. Your RH is perfect for a plant in later flower. I do agree with @CrowMaster the other poster that the temps are a bit high, if you can lower then perfect if not, work with what you got. I think a lot of plants would not like them that high but you seem to have a good one here that's dong well in them. try googling VPD cannabis chart, It gives you a "sweet spot" area of where to be in terms of temps and RH in your growing progression, much like a battle ship grid. Hope this helps Happy Growing!