Registration time seems to be more straight forward. However, often a time of a particular type is denoted by tx where x is the first letter of the type. As r is commonly used for denoting a relation, adopting registration time creates a conflict (-E2).
Extrinsic time is rarely used (-E3) and has the same disadvantages as intrinsic time.
Finally, physical time is used infrequently (-E3) and seems vague (-E8).