Why your guide does not start the grub-btrfs.path service at all?
The new snapshots will only appear in the grub menu when the grub/grub.cfg is updated,
and btrfs.grub is not doing it without that service running.
timeshift-autosnap also has an option to do this without the path unit.
may because I do missed to add that part ?
will this interfere with grub-btrfs path service?
You don’t want both the path unit and the option in timeshift-autosnap enabled. That would have it running twice for every snapshot. You should pick one.
I forgot that updateGrub - if set to false grub entries won’t be generated.
Not every snapshot. Manual snapshots are unlikely to trigger a grub update without path service?
As i do not use BTRFS at all I do only try it on testing environment.
So if there is something should be changed or added on the WIKI entry I mentioned:
please give a hint 
That is true, manual snapshots will get added to grub the next time it is run. If that is better or worse behaviour is somewhat of a personal preference.
So that it is not unclear to the reader:
My bad. 
I forgot that timeshift autosnap also creates grub entries.
Your original guide is fine.
It’s short and to the point.
No need to make it complicated, if one don’t need to see manual snapshots in grub straight away.
And they should appear there too, after the timeshift autosnap is executed next time.
Really interesting. This helped me a lot.
Thank you.