[yardstick]

Depending on the job, being punctual can be critical to keeping customers happy.

If I’ve got a major customer complaining about a critical issue and has scheduled a call with various stakeholders (including us) to discuss/resolve it, then we can’t miss that call. Nor can we reschedule without extremely good cause.

[bippihippi1]

If the disability affects a core job role then there are no reasonable accommodations. A blind person can't be a fire lookout, but they can be a host/greeter even though most customers would like to be acknowledged when they enter. the workplace just needs to make some changes to help the person.

also I'm not sure if 'customer wants the person not to do something' is undue hardship. If the employer says my customer wants to work with someone who can see my face when I talk, does that mean that employer doesn't need to accommodate blind people?

Like maybe the accommodation in your example could be to have another person on the team join meetings with you to provide a few minutes of coverage if you're late. If the job role really needs only one person to be exactly punctual all the time (does it really though?) then the eeoc advises to place the person in a different role with similar functions that aren't affected by the disability. read the guidance at eeoc.gov

Most of the time there are reasonable accommodations. It varies by person and the accommodations are specific to the role and person.

My point is that asking someone to just try harder is not the answer, and kind of ablist as it denies the reality of disability. Especially when you frame it as an accusation of laziness or an excuse to slack off.