Flares don't have a set time. It is true that CD is cyclical so someone can go through periods of remission and flares but more often than not rescue meds like pred are needed to dampen the inflammation and maintenance meds to control the inflammation.
If he is having new or worsening symptoms a call to the GI may be in order.
I remember you mentioned entocort and that he's been on it one week, that may not have been long enough for it to start helping or it may be that he needs to move to something stronger like pred.