It depends on what I am going for, but generally if I am going for additional FPs (have used 3 already), I will click on the next available time slot to check for any FPs that are ready for us to use as soon as we are done with the current ride. Say, for example, if I am in line for 7DMT using my 3rd FP at 1:55pm, I will click back on forth on the 2pm and the 2:30pm time slots to see if there is anything available that we want to ride, and if 7DMT is available at 2pm, I reserve it and know that we can get off the ride and right back into the FP+ line. If not, then I will go farther out, say 3pm and 4pm just to check what availability is like then. Even if there isn't anything I really want to go on, I might reserve it anyway and then try and modify it later. YMMV, but I think modifying a FP to get a different one is a bit "easier" than just searching for a brand new one. Of course, take into account what other plans you have when searching times (parades, ADRs, etc).
I don't tend to use the broader time ranges except to get a general sense of what is or isn't available later in the day. I BELIEVE, if a FP comes up available for the ride, you can click on the RIDE ICON (not the FP time slot) and it will give you all the FP time slots available at that time for that ride for the remainder of the day. Helpful, for sure.