It’s over an hour a month, it adds up
But don’t forget the woman in question is giving over 3 hours a month to the department by coming in 5 mins early each day to get changed and having to stay behind 5 mins after her shift every day to get changed too. That’s 50mins a week if she’s full time, which she could well throw back in your face if you approach her.
If she works in the NHS and some people who arrive at work 5 minutes after her are still seen as being on time because they wear their uniform to work I don’t really think there’s a lot you can do really, because technically she’s arriving to work early every day it just takes her longer than 5 mins to get changed.
Also, you need to make sure she isn’t taking longer than 5 mins to get changed because she has a medical problem etc because then you’re going to need to make proper adjustments for her to get ready as she could say she’s being treated unfairly because of this.
I’m usually early for work because I hate rushing around last minute, I’ve very rarely been late for work and usually if I am it’s beyond my control such as my (autistic) dd having had a meltdown at the before school club because they’ve redecorated overnight and forgot to tell me. But I don’t expect everyone to arrive early and I don’t really care if people run a few minutes late either so long as they pull their weight at work.
You know her as a worker is she likeable and lazy because that will eventually wear thin with people or is she someone who slogs with everyone else all day? If she’s hard working I’d look at the bigger picture.
I think you have issues with the moaning person too tbh as she obviously thinks she’s senior to the department, she doesn’t leave when she’s told to by management which makes me think she feels she’s above the rules somehow.
Ignoring you and going home late is just as rude as coming in late to be honest especially when you have spoken to her about it. You’ve asked her to stop doing something she doesn’t feel she should listen to you and does her own thing.
So really you need to address both or neither.
Next time she brings it up why don’t you say to her I can’t discuss other colleagues and their needs with you as it would be breaching data protection laws.
Or better still tell her to approach her work colleague herself about it for an informal chat and if that doesn’t work to come to you for help with mediation.
She might suddenly think it’s not as much of an issue when she has to do her own dirty work rather than run to the manager to complain and that act all innocent unaware when the other worker gets pulled up on it.
Do you have monthly / weekly departmental meetings? Ask her to bring it up in any other business because then she can air her concerns and you can address them publicly then the balls in her court.
If she brings it up you could reiterate that everyone needs to be ready to work for 8am (maybe you would need to check with HR first where you stand with this legally) and thatbway no one has been singled out then you could also add that as well as arriving late staff need to ensure they are leaving on time. You could come up with a list of reasons such as and it stops the cleaners being able to do their work properly, you’re concerned it leads to poorer performance, it’s a fire hazard because everyone is expected to be off shift by a certain time so no one would expect staff there if there’s a fire, it breaches health and safety and lone worker guidelines etc. Then say you will be monitoring both in the coming weeks until the next meeting.
That’s way if it continues it can be brought up at the following meeting and you can then say you will be speaking to staff personally about this if they continue. That way if you have to speak to either colleague you’ve given them 2 months to get their act together.