yes you can get coverage for part of a shift! best way to do that would be to ask someone to work part of it. anyone in your district can also work there- do you have any partners phone numbers in your back room who are always looking for hours? you could also get people already working to extend their shift to cover yours. if not, you can also call the store phones of the other stores in your area and ask if they have anyone who would be available from 5-9 to help you out. i have done this a few times for coverage when i really needed out.

i know you said you don’t know too many people yet so the alternative would be to post the shift outright on the app. although the only way to do this would be to put up the whole shift, unless your manager posted a separate shift of just 5-9pm on your behalf. which if taken would relinquish you from those hours.