A very good question !!.
American Urological Association (AUA) guidelines recommend the surveillance after treatment as follows.
If the initial diagnosis was high risk non muscle invasive bladder cancers, i.e. T1HG or CIS, which I think was your case.
• Cystoscopy at 3 months
• Subsequent cystoscopy every 3–4 months for 2 years
• Then every 6 months until 5 years
• Life-long annual cystoscopies thereafter
European Association of Urology (EAU) guidelines have similar recommendation with life-long annual cystoscopies.
National Comprehensive Cancer Network (NCCN) guidelines say 10 year annual cystoscopies, then shared decision on surveillance.
www.ncbi.nlm.nih.gov/pmc/articles/PMC8261410/