It depends on where you are.  At work, fika is typically arranged for thirty minutes.  We always get an invite in our calendar, so everyone shows up in the kitchen at 15:00 (3 pm). So,  if we are on a call or meeting, we try to wrap it up before then. ;-) If it's for leisure, and you're with friends and families, then it's all up to you on what time to end your fika.