How long can I keep photosynthetic softies in a blackout?

[avoiding work]

I have dinos and need to start treating them. I would like to start with a blackout, but see posts that say not to do blackouts with photosynthetic corals. Could I get away with one if it's only with photosynthetic softies? If I can, how long can I do it for?

 

[Rtaylor]

They should survive at least a week (they’ll be mad, but won’t die)