I'm also in MN, although south from you.
I get infant calls weekly here and do not hold infant or toddler spots at all.
I will hold a preschool spot for up to one month with a 2 week deposit. The deposit is non-refundable if they change their mind during the enrollment period, otherwise it is applied to the last two weeks of care if a written two-week notice is provided and no outstanding balance is due.
Anything longer than one month is at full rate to hold the spot. My rates are all FT and tiered by pick up times. They are welcome to choose the lowest rate.
I know since your just starting out, you want to quickly fill your openings. But, imho, it doesn't make sense to short change yourself financially for that coveted infant spot.