Fans really need to be on from day one of growth and far more than 15 mins a day. Try 12 hours a day and if it is oscillating so much the better.

Turning it on this close to transplant time may not help much but it sure can't curt them.

Dave

I leave the fan on low all the time in my cold greenhouse & it works well. You can also run your hand over them touching lightly at the tops of the plants.

More light, less fertilizer & cooler temps make the stems thick as well as the air movement.

My brother gave us some giant pumpkin starts with thin tall stems that had a rough ride in the car on the 2 hour drive over here because the stems were tall & thin. It's way too cold for pumpkins until at least June at our place, so I rigged up temporary accommodations inside the kitchen.

I slipped the peat pot into a tall slurpee cup along with some chopsticks & stacked the cup on stuff to be 2" under the over the range fluorescent spiral. They've greened & thickened up a bit as well as grew another inch this week. So far the stems appear to be healing & I will add more soil in the cup this week.

There's hope for thin & spindly seedlings.