Hi
I'm not sure if this is helpful, but the original design we did of
replay, which I'm not sure was ever captured in any of the internet
drafts, was that a subscription was only either a replay subscription or
a real-time subscription. You got a replay by specifying startTime.
There was no stopTime as this was implicitly "now" for a replay
subscription (ie, the time the subscription was created). Not specifying
startTime gave you notifications as they happened. This is simpler, but
was also in a universe that supported interleaving and multiple
subscriptions per session.