Well, I know for one thing that it's
RBY/FRLG > 3 years > GSC/HGSS
RSE is in a whole different region. There's no way to specify any time frame between the events of RSE and the events of RBY/GSC and remakes.
B/W > 2 years > BW2
Since all the Gym Leaders from all regions appear here, I'd say this occurs at least 1 year after GSC + remakes. That would mean that RSE occur around the same time as GSC + remakes, if not a little later, but no more than a year.
DPPt cannot occur at the same time as GSC + remakes, because Jasmine makes her appearance in Sunyshore and in contests. Therefore, it is possible that it takes place around the same time as RSE, or prior to GSC + remakes.