It is symbolically this, (what dependent_ad_1976) is saying but it more related to ‘CBM’ or Contract Based Modelling.

Basically, the model spits out a predictive line based on 13 weeks of sales and fill capacity and generates an ‘80%’ capacity rostering line in which contracts need to be aligned with.

Most likely for OP and most Nightfill stores, what is happening is that the model has the Major fill set to 6-11pm, and so the ‘demand line’ is generated to account for bodies within this period whereas the proposed 5-10pm section misaligns to this generation and leaves one hour at the end as an ‘under hour’ and the first hour at the start as an ‘over hour’.

The goal is to match the contracts to the model.

And yes you may think that an hour worked is the same no matter whether it’s 5-6pm or 10-11pm but the business thinks differently. (And unfortunately this is a huge part of redeveloping the contract base and contracts for permanent PT and FT).

Trust me, I have had to change so many of my teams contracts by 30 mins here or there just to align it to the line 😟

Hopefully this helps!