Hi gdr41,
I'm not sure about bamboo but vegies I start indoor I'll leave under the fluors 24/7 until there ready to go under the big light. You might also consider getting the light closer too.

GDR,

For most plants I set my timers to leave my lights on for 16 hours and off for 8 hours. Many plants actually need a dark period for proper functioning. However the length of the needed light period and dark period depends on the photoperiodic responses of that plant variety.

For some plants the critical factor is day length and for others the critical factor is night length. You might want to Google search to find the light preferences of your bamboo seedlings. They might benefit from overdriving your fluorescent fixtures, so that your bamboo seedlings receive more foot candles of light when the fixtures are on.

Ambient temperature could be a factor. Another factor is the volume of growing medium that is available to each plant. Maybe your pots aren't big enough and your plants have become severely rootbound. Nutrition is another factor.

MM

Trays should have enough space.I set the timer to 16 hours today.I'll see if I get any growththis week.

I'm not sure about bamboo either, but I agree with everything MarineMan said. I keep my lights on for 16 hours, 8 hours off at night and only adjust it for the daylight sensitive plants that need longer or shorter daylight hours. If you haven't started fertilizing yet, you can start once they have 1-2 sets of true leaves.