Compute wall_time using the monotonic time.perf_counter()

[hartelys]

Fixes #3808

Summary/Motivation:

This PR is intended to solve the fact that the measured wall_time is sometimes negative due to the usage of datetime.datetime.now(). It resolves #3808

Changes proposed in this PR:

• Instead of relying on datetime.datetime.now() we now use time.perf_counter as proposed in Negative wall_time exception #3808

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