I'll clear a couple things up.
1. If you hit the SOS button, the inReach will take your actual location (not your last 10min track), so the "tracking interval" isn't tied to your safety.
2. When you turn on/off tracking, you'll get a "start" or "finish" - I also send a preset inReach message saying "I'm starting/stopping my day here" - so for your IBA ride, you'll have an accurate start/finish.
3. As Steve said, it will send your last location IF you have tracking turned on and shut off your device.
4. You can send an unlimited amount of preset messages for free
I have my inReach connected to Spotwalla so I can easily share it, but you can use Garmin's website to share too.
Here is my last ride:
https://spotwalla.com/tripViewer.php?id=18cd65af2d86289ef7&hoursPast=0&showAll=yes
Notice that I have an "S" for start, plus a gas stop preset message in Fargo. This indicates to the certification gods that I'm starting here, with gas. Each gas stop along the route (Sioux Falls, Omaha, etc.) has another preset message indicating it's a gas stop. In Cedar Rapids, you'll see an "F" plus another gas stop, indicating that this was my final stop (that also had a gas stop).
If you were doing a rally, you'd simply adjust one of your preset messages to say "bonus location" - this will mark that location, even if you just had a "tracking interval" dot 2 minutes before.
For your 50CC I would turn on tracking at the start, hit a preset gas message, ride, hitting a preset gas message at each gas stop, arrive to your hotel, hit a preset message saying "I'm starting/stopping my day here", turn off the device, then in the morning, turn on the device, hit the same "I'm starting/stopping..." message, then continue riding, at the end, hit your "I'm starting/stopping my day here" and a "gas" preset and you should be just fine getting it certified.
I found that
Jim Cyr at avoidingchores.comhas some absolutely amazing videos that cover both the original and Garmin inReach