This sounds similar to commercial "traffic". You want an event (or group of events) that stays at an approximate time irrespective of what is manually loaded earlier in the schedule.
A bit like the way that the fixed time marker works in manual assist but instead of it being "pushed down the list" by tracks manually added before it, the event stays at the earliest time it can by "jumping back up the list" over manually added tracks.
No, I don't know Sonicart I'm afraid.
From the name (and a little background knowledge of the industry) I guess it was a replacement for the old ITC triple stack cart machines that were the staple of UK commercial radio a few decades back. These would trigger each NAB cartridge in turn by use of a "secondary cue tone" so the tone at the end of the first cartridge would play the second and so on.
I now get what you are trying to do (although I don't see how the announcements are scheduled) but I can't see any way of getting PlayIt (as it now is) to do this.
Essentially this should be a feature request.
It touches on a potentially complex matter, the scheduling of composite events or material other than library songs (for example whole recorded programmes).
This would be a great feature!
Even better would be if the "music fill" in "Semi Auto" or "Auto" would make a selection (within the rotation rules) that put "Commercial Break" items at the right time (within say a minute).
Our community radio station uses Jazler to run stopsets. We have used it from our inception 13 years ago. You can cue up any number of spots ('collect') and then set it to sequence. Start the first spot while sequence is active and it plays the entire stopset. The latest version now has two players so say a top of the hour stopset can be readied and maybe another stopset for the bottom of the hour. It good for jingles too. Our experienced and otherwise on air talent all find it intuitive to use. Here's a link for more info: https://jazler.com/products/show.asp
I wish to load,but NOT play,several tracks at a pre - determined time... e.g. load 3
tracks at 11:58 and have them manually started at say 12:00.
Is it possible to do this in Live Assist Mode, and if so is it done in Manual,Semi Auto