Babysitter Needed for my Children - Now Hiring

We are looking for a backup sitter for when our nanny calls out sick or is on vacation. Unfortunately, this is usually a last minute request and understand if it cannot always work out. My wife and I both work full time and would need someone from 8am-4 p.m. on the days our nanny call out. Must have experience with infants. We have a 5-month-old. Required to feed, change, play with, put down for a nap, take on walks etc. We have a 2-story condo so must be comfortable with stairs.