8 to 10 hours straight should be fine.
If you have multiple tubes then a midday burst works well.
Let's say you have 4 tubes.
2 tubes for 3 hours,
4 tubes for 5 hours,
2 tubes for 2 hours. 10 hours total.
This is what I do and I have no algae. I don't have any algae-eaters either. Good CO2, EI, tank maintenance and plenty of plants is a great defence against algae.
Siestas are best for poor CO2, but as mentioned, good CO2 is much better.