One way to use 10 Backup tapes (or drives) could be having each tape begin a single day. Leaving you with 10 tapes equaling 10 days.
Another way to use the 10 tapes would be 4 being work days and 6 being EOW (end of week). This would leave you with the last 4 days plus last 6 weeks, not bad.
The best way I’ve found would to make 4 tapes being work days 3 being EOW and 3 being EOM (end of month). This way you can have the last 4 days, last 3 weeks, and 3 months. This rotation helps prevent any anomalies (within 3 months) from every becoming a problem.
in short you can use 10 tapes for 10 days or 3 months you decide.