It depends. For example, a SaaS with highly transactional sales at low B2B contract price like $6k ARR each transaction. Your mileage may vary. You may have to try other formulas depending on your average selling price and overall annual sales quotas.
For monthly recurring contracts, for example, the first month actually collected goes to the sales rep, some pay it over 6 months and some pay it monthly for first year, but no longer than 12 months. (After 1 year, it’s retention and someone else’s responsibility.). If it’s a low contract value, the whole commission is better paid up front for psychological reasons. It is best to talk to a sales coach.
If your sales rep is responsible for both sales and retention, you might consider paying a percentage in second year for retention, but lower percentage because keeping customers is theoretically easier than winning them in the first place. You can offer it monthly or annually, with small financial incentive for up-front annual.