-I made this for reference 

-So hc that Be More Chill starts sometime in September.

-Jeremy takes the SQUIP around the last few weeks of September.

-'More than Survive' reprise takes place over a few weeks than an actual day.

-Then 'Upgrade' is a day long and around a week passes before 'Halloween'.

-After Halloween it's November and 'The Pants Song' 'Pitiful Children' and 'The Play' take place during the first week of November.

-Then Jerm is in the hospital for like a few days till halfway through the second week of November.

-'Voices in my Head' takes place the last school day of the second week of November.

-So yeah in my book BMC takes place over three months.