Confusion over job role

Starting my new job as an online assistant next Monday, but the job role and job hours seem conflicting.

During the interview, I was told I would be an "On-Demand" Online Assistant, meaning I'd handle Deliveroo orders etc and wouldn't be a part of the regular picker team.

Although what confuses me is that my earliest shift start is at 5am, which is 2 hours before the shop opens, so I don't see how I could possibly do my alleged role when the shop isn't even open to order from.

Is it possible I would be switching between the roles depending on what time my shift starts or was I told the wrong thing?