I’m not a huge proponent of trying to keep them at a perfect temperature, or the 5 degrees a week thing. I think the best and easiest is to have one area warm enough, even if it is a little too warm, and have other areas too cool so they can find their own comfort zone in between. They are living animals. Just like many humans cannot agree what is the perfect temperature in a room, individual chicks can have different preferences too.
I’ve put 5 week old chicks in an unheated coop with the overnight lows near freezing, but those were standard sized chicks, not bantams, and they had been acclimated to colder temperatures in the brooder by letting the far areas really cool off.
But to play along, if you go by the 5 degrees rule:
0 – 7 days = 90 to 95 degrees
8 – 14 days = 85 to 90 degrees
15 - 21 days = 80 to 85 degrees
22 – 28 days = 75 to 80 degrees
29 – 35 days = 70 to 75 degrees
36 – 42 days = 65 to 70 degrees
If they are 36 days or older, looks like they are about ready. Or if you want, use a 60 watt bulb instead of the 250. They won’t need it but it will make you feel better.