@Mr. B Welcome to Microsoft Q&A, Thank you for posting your query!
Firstly, apologies for the delay in responding here and any inconvenience this issue may have caused.
There is no such timings for creating a snapshot but it should complete in a couple of mins(based on the size). Same is the case for creating a disk from snapshot.
A snapshot is a full, read-only copy of a VHD. This itself means it's hydrated
Hope this helps!
Kindly let us know if the above helps or you need further assistance on this issue.
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