What did you mean when you did the unit conversion with the $T$ on the bottom?

This was a calculation of the quantity ``how many rotations in 7.00 days''. (It was not only a unit conversion, although it included a unit conversion.) The number of rotations in 7.00 days is 7.00 days, divided by $T$, the time for one rotation. But if $T$ does not have units of days, then you need to convert units so that numerator and denominator have the same units. I converted the numerator to seconds, and the denominator $T$ (which we were given in ms) to seconds as well.