I think they’re active til the last day of the month.

They're active until the last day of the month in which you quit. For Cobra I believe you have up to 90 days after leaving your job to opt in, the company should automatically send you a packet with all the info, and you can use cobra for up to 18 months until you become eligible for health insurance elsewhere. Cobra is a great option while in between health insurance plans but you are paying 100% of the premium instead of pay around 20% while Starbucks pays the other 80%. Alternatively, you could also look into your state sponsored insurance plans and apply for coverage through their marketplace where it will most likely be cheaper.