Yes, we do support custom escalation times. You can set the amount of time that the Primary on-call has to respond to an alert (after which it is escalated to the secondary). Likewise, you can set the time that the Secondary on-call has to respond to an alert, before it is escalated to the tertiary.
This is configurable under the Settings tab.
I really like this service and should the escalation change I would sign up in a heartbeat, it's exactly what I was looking for.
We left a comment on UserVoice, but I thought it couldn't hurt discuss here.