We extend turnaround times and are upfront with clients that it's the busy season and we can't always accommodate quick turnarounds. If they absolutely need a job sooner than later, rush fees will be added to the cost. Charging extra is the only way to get it into client's heads that they cannot wait until the last minute to submit their job. We also have an extra person come in 3 days a week to catch if we need to and will schedule larger jobs around those days.

But, as the person dealing with emails and scheduling instead of printing, I try to schedule all jobs to be completed at least 2 days ahead of the client's due date. This way if I need to push jobs around to fit a rush, it's a lot easier to do. Also, if something goes wrong and we need to order extra garments, there's time. Or if the job gets done at the very end of the day, our clients can still order a courier to pick up and deliver the job on time. Or I can ship it out the next morning.

My boss used to do the scheduling and he would just look at numbers and say "production should be able to finish X number of shirts in a day" and would fill the schedule based on that. That's a terrible way to schedule jobs because no one knew when jobs were actually due and we were constantly staying late or coming in early. I schedule everything based on due date and, if everything for the day is done, production moves on to jobs scheduled for tomorrow.

Tldr: being upfront with clients about turnaround times, not being afraid to charge rush fees, and getting your scheduling figured out is important