Not to worry! I'd add the cal-hypo by dissolving it first in a 5 gal bucket then pouring the solution in front of the return.

As long as the cal-hypo crystals don't touch the Tri-Chor stick you are fine--dissolved in the water, chlorine is chlorine. So you can add it immediately, even before removing the tri-chlor sticks from their feeder.

If it were me, I'd take the sticks out completely and save them for the travel time.