In my 60l - 10am to 10pm. I know it is too long but the reason for that is because I manually put the CO2 on (I know I should save up and get a solenoid) before I leave for work around 7:30 and I don't want to leave the CO2 running for too long without the lights. The light is only 15w t8, so it works fine for me - no algae etc and my plants are doing OK.
In my 30l fluval Ebi - 5pm to 11pm. This is a new set up, so still in 'suck it and see' phase. Had it on for 3 to 11 but getting some algae issues so I reduced it by couple of hours last week. No CO2 injection in this one, daily dosing of .5ml excel and .5ml tnc complete.