To be perfectly honest with you , I really dont fancy the idea of adding a percentage on if they are late,
yes it sounds ok, but I dont want to upset my custys by charging them extra, sometimes they have just needed reminding, sometimes they plain forget

but what ever the reason , putting it into practice imho is asking them to look elswhere to have the work done .
When do you enforce the extra charge? a day late, a week late ?
No ill, stick with 5% off if paid in full .
geoff