If they were $1.99 each I'd just drain the water and throw them in anytime.
If they were $10 each I'd temp acclimate and throw them in at least a few hours after CO2 went off for the day.
If they were $30 each I'd actually adjust my CO2 levels over a week or two to slowly bring them up to speed.
But that's me.
Of course, regardless of cost, I'd have quarantined them for a few weeks. No sense in killing off the rest of the fish in your tank.