For obvious reasons, it is good to keep your stock up to ensure you can deliver on your jobs. The other reason is your costs stay in line, so you are not spending more than you need. Short turnaround on coil delivery can add more value to the project eating away at profits.
When is a good time to order?
Depending on the volume, you need to plan like you are buying an airplane ticket. For large quantities of 100 binding coil boxes or more, you may want to give yourself at least three weeks ahead of time. One, it ensures the best price possible and two, your project will run on time.
For smaller quantities of a binding coil, you should be good up to 7 days before your project starts. If you order up to 20 boxes, it should not be a problem getting it in time for your project to start. If your items require shipping, remember the cheapest shipping days are Monday-Friday. If you need weekend delivery, it is going to cost you. 2-day shipping is not much better.
In Myers-Briggs terms, the person that has the personality of XXXJ is the one you should task with planning your projects. They like to work with lists and making deadlines is what they live to do. If you hate lists and hate planning, give it to the person that does.
You will make more money on you project leaving very little to waste.