The last instalment always lands on your order form close date.
The earlier instalments are spaced out as evenly as possible between the day the order was placed and that final date, with a few guard-rails so dates make sense. Generally the first payment is about 14 days out; the middle one sits halfway between the first and last.
If your timeline is very short (e.g., less than a week per instalment) we simply make all instalments due on the final date so buyers aren’t asked to pay twice in the same week.
Instalment amounts are split as evenly as possible; any odd cents go on the last payment so totals always match.