You can keep the lights on full 8 hrs..no problem with that, but there are few concerns..few +ve and few -ve.
1> algae will eat all nutrrients like NH4, NO2, NO3, PO4 etc, so water will become very safe.
2> whenever there is algae growth, copepods and amphipods are inevitable. They feed on algae and breed and multiply rapidly in bulk numbers. This will create great bio diversity and zoo plankton reserve for future.
3> many other small photosynthetic organism which came along the rocks etc may start growing. Coraline algae can grow if right alkalinity and calcium levels are maintained.
1> Too much algae may fowl the display. Too much cleaning involved
2> Algae will utilize most of the NH4 and NO2 for growth , hence NO3 creation or nitrification will be hampered as bacteria responsible for it will have to compete with algae for these nutrients. Bacteria colony may shrink, later on adding too many fishes at once may increase the bio load which the bacteria colony will not be able to handle and sudden ammo spike may prove fatal.
Hence I suggest keep the lights on for 2 to 3 hours a day. Not more than that.
Thanks & Regards..
"If you want to do something in a better way, do it yourself !" --Nepoleon Bonaparte