Rochester, MN:
Marriott.com indicates that the lounge is closed on weekends.
I checked in last Saturday afternoon and asked anyway.
First I was told that the lounge had been trashed during breakfast service on Saturday morning and would remain closed for the remainder of the weekend as as a result. A polite request then resulted in breakfast coupons for two.
An hour later I received a call in my room informing me that the lounge would reopen on Sunday morning. Sunday lounge breakfast included eggs, bacon, oatmeal, fruit, etc.
In summary, this lounge appears to be regularly open on weekends.