you coulds "flowre" them before they have roots.. menaing, you could set the lighting period to 12/12 befroe they have roots..

but what would be the purpose...? What are your intentions? I am curious.. : )

To shorten the budding period?
This will not shorten the budding period/plants life cycles (plants life from begining to HARVEST) and may actually prolong the process ...

and will definitley reduce YIELD..

: )