Kim, it's usually dependent on the clinic policy. That's why, when i started looking for a clinic, i made sure that they are open every day, no matter what.(maybe not if a hurricane hit the area

) On weekends and holidays, they only do insem's and ivf's(u/s also if time sensitive), and are only open for a few hrs in the morning, but it's enough. If you can find anywhere else, you might want to switch. You are paying them to help you get preg, not to have them say sit and twiddle your thumbs for the next 2 months because it's not convenient for them.
I'm using frozen donor sperm as well. No luck yet.

This is my 4th cycle, and i have my next iui's this mon. and tues. I keep telling myself, another dad-popsicle, another chance.
I am very fortunate that i live in an area where there are a lot of clinics to choose from. Also they are generally open to helping single women, because so many unmarried women want a baby before their time runs out. I hope you can find a solution.