Numpty >>
szerda augusztus 18 - 13:52 Base build time for Stadium 10 is 109.5 days. With a CM level 10 this reduces to 76.65 days.
Another level 4 CM will reduce that by a further 12%, which is 9.198 days, so you wouldn't gain anything by waiting 9 days.
There's no need to fire him either. You can employ a 2nd CM at any time and when it works correctly the bonus is recalculated. (The bug occurs on removal which is when you might need to be careful.)
In my opinion you'd probably be better off keeping the 2 fan shop staff anyway. The extra popularity is probably worth just as much as saving a few days on the building time.