My honest opinion is that it does sound a little harsh. If I'm a client that is always on time then sharpening the late fee may feel like you're looking for more money.

I would suggest that you deal with the person that's the issue on an individual basis. If there's one person that's taking advantage of it then I would suggest that you change their late fees.

If it's more then one person then I would suggest that you look at what you're doing. Are you enforcing it strong enough? Are you letting the clients know that late pick ups intrude on your family time. Have you told them that it's not acceptable and your closing time is your closing times.

I don't enforce a late fee because in my mind, enforcing a late fee allows a client to think that it's ok for them to be late, they just pay a fee for it. I simply don't allow lates as a rule.

The odd time a client will ask if I can keep johnny a few min later in case they get stuck in a meeting. Some days I can and I let them know it's fine, but I confirm a "by the latest " time and some days' I can't and I tell them that.

I guess it depends on your clients.