Ugh, those 90-day windows are the worst! We had a client last year who stretched to almost 100 days. It made our cash flow so tight we couldn't order supplies for the next job. Now we do a 50% deposit before we even open a project file. It's the only way to keep things moving without going into debt.
Seriously, my buddy's print shop got burned by a 75-day term from a "big client." They had to take out a short-term loan just to cover payroll that month. Now they won't even answer an email without a signed contract and a deposit.
Saw a 105-day window once at my old shop. Totally get the cash flow panic, like Alice said. That's why we moved to net-30 with a late fee, no exceptions. Stops the bleed fast.