I assume your flight is VFR, therefore all that is required is PPR for Islay, PPR for Oban, and PPR for Benbecula. They will not be strict about times, however the AIP effective from 4th May gives operating hours 12.00-16.00. This at Benbecula. That is quite restrictive from what you appear to want to do.
You would require an out or hours permit from HIAL, costs app 35.00, which will allow you to arrive/depart, when you wish, but let them know you are going. Call HIAL at Inverness and they will organise for you. (This for HIAL airports only. Oban is not one)
Scottish info is precisely that, information service, and IMO you will not require the filing of a flight plan, unless it goes IFR, in which case, you would follow the IFR arrival procedure, as per your filed IFR flight plan. IFR only for Islay and Benbecula, Oban does not have a published procedure. You would want to do the flight VFR though, for a good number of reasons.