calculate pre-assigned days per month from a file, which works on a daily basis and collects figures over an interface

[TonyPro]

I am looking for a working formula to calculate the number of days a shop is open. Opening days are usually Wed til Sat, but shop could be open any day, according to business needs. Formula need to be embedded in a excel workbook, which is collecting information's through interface. Workbook has to be re-run once every day. Formula should be self sufficient and zero or at least as little as possible, manual input is necessary. Workbook works with amount of days/month, day of week and date, time not necessary.

I cant supply any formula because I haven't found anything which I'd need as of yet.

Thanks for helping,
TP