I wouldnt say everyone is completely different, there are some patterns in ibd, too much refined sugar usually causes more symptoms, and less fiber can make things worse.
when you will notice will likely be different though, it could be 1-2 hours you feel pain or movement sensations, or it could be a few days.
There is something called an elimination diet which is used for people with food allergies, where you follow a basic simple diet, then slowly add foods for a week to test them. its a little extreme and youll need to make sure your starting diet gives you basic nutrients. But read about SCD diet, ibd aid, cded, and fodmap diet, all these versions of diets used for ibd can give you general patterns as to what might irritate symptoms.