My very first flock of RIR started at 4 months! I was shocked and surprised, not expecting eggs until 5 mo. Every collection had at least one double yoker for weeks and weeks.
Don't worry about the hatched chick. It is fine up to 3 days. It's always very risky to open during lockdown. Is there anyway to add water through the vent whole? From my understanding you need both vent holes open now for air.