How to properly name record creation(insertion) datetime field?

Why not just use plain on Created, or CreatedOn. Windows OS uses three date properties for files.

Created:
Modified:
Accessed:

So you could try to keep that sort of convention if you prefer.

I tend to InsertedDateTime and InsertedBy (and Updated%, Affected% for indirect updates perhaps, Deleted% for logical deletes).

OperationDateTime for general auidt table

If I was storing a date only, it would be StartDate. Likewise, time only would be BookedTime

Another rule is to avoid "SQL" terms, so Added/Changed rather then Inserted/Updated. I inherited Inserted/Updated and it's consistent at least

Just be consistent: no mixing Created% with Inserted% with Added%

I always use CreatedDate in these circumstances, and it gives a template for other dates: UpdatedDate, DeletedDate, PurchasedDate and so on.