Business Hours methods have been turned into installable Flow Actions here: https://unofficialsf.com/chris-van-der-merwe-work-with-business-hours-via-new-flow-actions/
There’s also a Salesforce Labs package here: https://appexchange.salesforce.com/appxListingDetail?listingId=a0N3A00000G0tuMUAR
Sean Dukes wrote a good post on using Time here https://unofficialsf.com/building-a-declarative-time-picker-and-working-with-time-in-flows-and-how-summer-21-helps/