I use the second hand on my watch to help with mixed strategies; sometimes using it to inform size of raise, or the direction of raise/fold, raise/call, and (rarely) call/fold decisions.
As such, if you happen to notice me look at my watch, you can deduce I might be raising, or calling, or folding, with a strong, weak, or medium hand that is already made, or on the come; or that I am interested in the time for a reason such as wondering how long i've taken, how long i've been at the table, if i need to leave, if a new dealer might sit and collect time soon, or something else.
I get that you're a pedant who wants to be right; but it's not a remotely useful tell unless the person does it only in one type of situation. but nobody who is concerned about how well they mix a mixed strategy is dumb enough to mix only _one_ strategy.
edit: and i'm not a pro. i play in mid-stake games with $1-5k buy-ins.
The point was that if you're going to look at the clock and use the second hand to help you make decisions about whether or not to bluff, look at it at other times too when you're not making a decision, so that looking at the clock doesn't become a tell.
Some pros use systems where they look at the second hand of a clock to decide whether to bluff or not, as a proxy for randomness.