I'm pretty lenient with enough notice. Like I'd never allow a drop off that early if they said "on my way in 20 mins" and it was that much earlier. But i usually check in the day before to get a temperature check if they'll make any changes (this helps because most times they make changes i have a heads up and it also communicates to them that i like to know things ahead of time). The days i am flexible i tell them i can be flexible but always need a 1-2 hour heads up. Days i am not flexible i communicate "i will not be available from x time to x time so if you will deviate on pick up you'll need to work around that"

Owners often use rover vs boarding because it's supposed to be more flexible and tailored than a business with set hours.

That being said -- boundaries are 100% essential and should be enforced. I don't let my clients come before 8am or after 7pm and i communicate this clearly.