It has to be 240 hours over 3 calendar months, an average of about 20 hours per week. You can check your eligibility at
$1 or call the partner support center at 888-SBUX-411.
When you initially qualify for benefits you'll get a letter in the mail with your deadline to enroll. If you've received that letter and then missed your deadline, you'll have to wait until open enrollment in September. If you met the requirements to keep your eligibility, you'll get another letter soon reminding you to enroll. That's if you earned 450 hours total from January 6 to July 6.
You can get more info by logging into partner hub and going to the benefits section; you don't have to be on a store device to see all the info.