10-15 minutes before the pack drops, a queue is opened and you join the queue. At the time of the pack drop everyone who was in the queue is assigned a random number and that number is your spot in line. Whether or not you get a chance to buy a pack completely depends on the randomized waiting number you have been assigned.

For example, there was a Rising Stars pack drop that was limited to roughly 32,000 packs. I believe there were 190k users in queue. So you would need to get lucky to get a spot in line between 1-32000 (sometimes very lucky).

It does not matter how early or how late you join the queue as long as you are in before the official pack drop time. I’ve seen several posts of users who are upset that they joined the queue as soon as it opened and still got a shitty spot in line, but it’s all randomized.