You can try a couple of methods:
1. Use editcap "-A" and "-B" option to create a new file with packets only between the two timestamps. Then, open the new file in wireshark.
2. You can use wireshark filter something like this:
frame.time > "Aug 20, 2008 01:34:13.000" and frame.time < "Aug 20, 2008 01:34:24.000"
Adjust the times according to what you want.
You can also filter on time relative to first frame using "frame.time_relative" if that is easier. Lookup "wireshark-filter" manpage.
Hope this helps,
- Abhijit