Let it bloom then snip it off. It would be better for the roots to do it now, but letting it bloom won't kill it.
When it's suggested to remove buds, that's the optimum thing to do for faster root and plant developement. Not doing so just lengthens the time it takes for your little cutting to get bigger.
Letting it bloom may actually help with feeder root developement as blooming demands more moisture and nutrients. The harder it tries to support the bloom the more roots it grows to take up these nutrients and water.
At the same time though, this energy could be going into making a stronger plant.

I always let mine open one blossom..mostly because I can't stand not seeing the bloom, but I tell myself it's to make sure that I have the correct I.D. !! It won't hurt it..enjoy your blossom, just pinch the other buds out. Donna

I'm with Donna.
If it's something new to me, in particular, I can't resist seeing one bloom open.
Then I'll harden my heart and pinch off the rest of them.

Jeri