I interviewed at Brex, and they required getting online within 5 minutes of being paged. (I did not get the offer, but I would not have accepted the offer after learning that.) Where I currently work the response time is "ideally within 15 minutes", which is a lot more manageable, since plenty of places I like to go are within 15 minutes of my house. My job pays more than average because of on-call, it's 1 week out of 6, and there's probably an average of 1 call out of business hours per week (mode is 0).