Undertaker's recovery time is expected to be around eight weeks leaving him available for a return in mid-July. The talk still as of now is for him to wrestle at SummerSlam in August giving him an extra few weeks to prepare and use TV time to build up his return to the ring.
There was a plan at least at one point to hold off his return until the newly named "Breaking Point" PPV in September (which was originally known as "Unforgiven"). The theory was that Unforgiven had an Undertaker-type theme and saving a return to boost that PPV would help, but this had been done before and Unforgiven ended up bombing. So the idea of an Undertaker return boosting PPV buys doesn't appear to apply anymore since he has had so many returns in the last few years.