Coronis
In lucid awakening
HGSS takes place 3 years after FRLG, and ORAS takes place 4 years after RS as well as 9 years after the Salamence event of Ruby and Sapphires childhood, which is at the same time as RGB. This puts them at the same year, with HGSS in the spring/summer months and ORAS in the winter months (as evidenced by Norman's Sawsbuck). Too bad the SPedia made a mistake listing Crystal's age in HGSS (they mistakenly listed it as 14 which is impossible), otherwise we would have a better approximation of HGSS's month.
As for BW and Platinum, the hint comes from the SPedia's timeline. It lists Hugh's childhood encounter with team plasma (which is 5 years before B2W2 and thus 3 years before BW) as after platinum. This means BW is at least 3 years after platinum, though it could be even longer.
As for XY, it's certainly not the same time as ORAS. Although there is no clear time lapse listed in the SPedia timeline, they are listed in natural chronological order which means it must come after B2W2, which is quite some time afte ORAS. This is in line with Diantha's apparently young appearance in Steven's flashback of Kalos in ORAS.
Coronis~
As for BW and Platinum, the hint comes from the SPedia's timeline. It lists Hugh's childhood encounter with team plasma (which is 5 years before B2W2 and thus 3 years before BW) as after platinum. This means BW is at least 3 years after platinum, though it could be even longer.
As for XY, it's certainly not the same time as ORAS. Although there is no clear time lapse listed in the SPedia timeline, they are listed in natural chronological order which means it must come after B2W2, which is quite some time afte ORAS. This is in line with Diantha's apparently young appearance in Steven's flashback of Kalos in ORAS.
Coronis~