SLA’s are tricky because they set a specific goal. Often, they are essentially a deadline applied to a series of steps in a process.
Which is worse, three customers who are a day late in getting a response, or one customer who is 3 days late getting a response? So the answer is that this is a trick question. It obviously depends on a lot of factors. How big is each of these customers? How finnicky?
SLA’s, like many goals, are easy to do wrong and very tricky to do right. When setting goals, my favorite consideration is this: choose goals that help people make tradeoff decisions. Goals are about priority, and priority is how we choose to invest in our most valuable work, or more importantly, what not to invest in.