considering bp's a very shy timid snakes it would be too stressful for them to be handled for more then 20 minutes at a given time. i've noticed that around that time my girl starts making a beeline for the nearest dark hiding spot. that's my cue that it's time to put her back. and the weather really has nothing to do with good/bad handling times unless your taking the snake outside for handling time...
from what i know the times when handling is a no-noare:
1) when you first get them, they need at least a week or two to settle in to their new home before any feeding or handling is done.
2) when they're "in blue" during the shed cycle (although i stop all handling during shed as soon as i start suspecting that my girl is going into shed.)
3) during the 2-3 days directly following a meal.
other then those times i handle my girl about 2 x's p/ week for 20 minutes each time.
keep in mind no snake likes being handled they just tolerate it. it has no benefits for them, just gives us the pleasures of "interacting" with them.