The place I’m going to says the only days I can go are at 7-10 days after the 1st day of period. However, online (through shady grove fertility) it says 5-10. Which should I follow?

My period can vary 25-28 day cycle each month and I won’t know which it will be until it actually starts. The place I’m going to only offers one time per day for the HSG, so if I schedule in advance and my appt ends up on being 6th or 11th and I try to reschedule I might this to wait another month 😔🙁😩