Hi Sheila!
Thanks for your question. Making
Disney Dining reservations is certainly the way to go. There was a time or two our family tried to "wing" it and just walk up to a restaurant for seating. A few times we got lucky, but the majority of the time required significant waiting, or no openings to fit us in, so kudos to you for making a reservation.
Whichever time you schedule, Disney asks that you be there at least 5 minutes before your dining seating time. For example, if I had Dining Reservations at
50's Prime Time Cafe for 8PM at
Hollywood Studios, I need to be there to check-in ideally by 7:55PM. Now, what I can say is the Cast Members working the check-in area typically offer a little flexibility. There were a few times our family showed up right at the scheduled time, and, in some cases, up to 10 minutes after our scheduled time. Although we never made a habit of tardiness, we never encountered an instance where our time was cancelled, so long as we came within close proximity of our scheduled time.
My recommendation is simply to plan enough time after getting off an attraction to make it to your dining reservation. This is even more critical if your dining reservation is, say, clear on the other side of the park! :-)
Have a Mickey Magical Day!
Terry