I havent used a popper in ages and from memory in really needed to listen carefully for 2nd crack.
I wouldnt leave the beans in an open paper bag, as soon as they are cooled place them into a one way valve sealable coffee bag to ensure they stay fresh. The valve will let the CO2 gasses out but will not let air into the beans.
I generally leave my roasts 3 - 4 days before trying, unless of course i have miss judged the qty i am using and nearly run out. I did a roast about an hour ago and only have about 150gm of roasted left from my last batch so i think i will be using a fresh roast tomorrow, if i do another couple of roasts then i can stock up and let them sit a few days be for. One way to see how the flavour develops is to sample a shot at say day 1, 3,5,7,9 etc. and you will see a change over time.
Chimney is a great idea, i also used to put a piece of wood over the top approx 50% to keep heat into the unit and that would ensure 2nd crack at about 8 mins or so.
Keep on roasting