>>136022269we don't have a good timeline in place for any of this
we know Millie and Moxxie have been married for a year by the end of S1, which suggests the business has been in operation for longer then that
its implied the business initially started assassinating targets in hell, before switching to only assassinating targets on Earth, which further elongates how long the business has been running
I doubt Blitzo's babysitter was Millie, considering the "founding" image of I.M.P. only shows Blitzo and Moxxie, and that Millie still needs time to have her failed relationship with Chaz
so we have at least 1 year between leaving prison and the present day, i'd guess its between 1 to 3 or so years