Found this previous post:
"Here are the dates of the past several application cycles when a waitlisted Tufts SDN student first got an acceptance call from Tufts (note: obviously SDN isn't an ideal/accurate barometer, so take this for what it is):
Thurs 5/28/09
Tues 6/1/10
Tues 6/7/11
Thurs 6/21/12
Thurs 05/28/15"
It may be awhile longer. But, take heart, during last year's cycle Tufts sent those they accepted an email asking if they wanted to defer in mid-May, so, by the looks of this thread at least that hasn't happened this cycle (yet).