You might try using running totals. Create a running total called countearly. Summarize your order number and do a count. Under evaluation, use a formula and put the formula that determines if the order is early. Repeat this process for ontime and late.
To calculate the early percent, create a formula:
(countearly / (countearly + countontime + countlate)) * 100
The ontime percent would be:
(countontime / (countearly + countontime + countlate)) * 100
The late percent would be
(countlate / (countearly + countontime + countlate) )* 100
I think this should work. To save some time, I would create one of the running totals and print it on the report to make sure it works. If it looks good, create the others and the percents.
Good luck.