time

It's a bit odd.

"When was the last time you..." generally gets you a date. This sounds like you called her on many different days, and they want to know about that day. What you did the second Monday, or the Tuesday of that week, isn't the point of the discussion.

A police officer wouldn't say "the first Monday in February 2006" but would say "on February 5, 2006" (or whatever

Thank you, GG. Is it possible to convey the same message with just one sentence?

Should I say, "What time did you make your last call to your husband's mistress on Feb 5, 2006?"

Yes. But it leaves open the possibility that she made a later call on Feb 20, etc.

New2Grammar

I think this sentence will solve your problem and that of the police officer.

What date and time did you last call your mistress?

Thank you, Yoong Liat. I'm sorry that I didn't make it clear that I'm only interested in knowing the last call made on a specific day, in this case, Feb 5 though there are other calls made on other days.

When was the last time on the first Monday of February 2006 you called your husband's mistress?
There are no grammatical mistakes in this sentence.

CJ