Hmmm. Try this. It may or may not be faster than reading manually from the stage/flow hydrographs.
1. Set your detailed output interval to the smallest setting, 1 minute.
2. Rerun your model. It may take a LONG time to post-process with a 1 minute detailed output interval.
3. Open up your summary output table and select All Profiles (except Max WS).
4. Copy an paste to a spreadsheet. Each cross section will have a number of rows, each representing a different profile.
5. Then add a column that takes the difference between the first WS El in the block of data and each successive profile.
5. Look in that row for when you get to 0.3 ft. That’s your arrival time.
Like I said, this may not be much faster than manually reading off the hydrograph plots.
Your other option is to write a program that automates this process, but that would be too difficult unless you have programming experience and you know how to control RAS externally.
Good luck.
Chris