Normal acting kitten with mild fever for one week, high FIP titer on Thursday , if FIP how long until more symptom show

I have 5 month old kitten, low grade fever for one week, bout of mild of the runs - just cleared up, titer came back "high", eating, playing, drinking like a normal kitten. If FIP how long before other symptoms kick in?

I am anxious ridden all day long, leaving him alone with other two cats, not knowing if he will be very sick by time I come home when he's fine in the AM...