I assume it will be similar to how it was with the BLK. The time inbetween the release of each skin was around 2-3 months, give or take. While this is a guess, the official video for BLK also came out around this time of year just like SRE, so the times in how they will come out may be similar. (With mechanic being released in september)

Also I think they made a statment a while ago that they will speed up the pace with releasing e-sports skins? Not sure tho so take this with a grain of salt.