The snooze tabs can be configured to launch at a time or date that you want it to. It can be opened later in the day, next day, after a week or next month. To get this feature, you can visit the link https://testpilot.firefox.com/. The page offers options to get the latest features on Firefox. You can choose Snooze tabs on this link and configure it on your Firefox installation.
Live....and Let Live!
As a Chrome user, I haven't tried this feature yet, but yes, this feature itself is quite interesting and undoubtedly useful for writers like us, as we work on different things simultaneously. In this way, the browser won't get overloaded.
There is no specific information on how many tabs you can snooze, but from the announcements in their official site, we can assume that the feature should be available for any number of tabs.
As it would work almost as closing the tab, or minimizing the tab, I don't think, there can be any restrictions for its usage, especially when the purpose of the feature is to close down unnecessary ones which would be automatically multiple in number.
But setting an Alarm for each of them seem to be quite difficult a task, as one needs to be highly organized and conscious to know his moods, his future timings. One should be able to predict his forthcoming situations, when those tabs would appear to be relevant again.