@Shulfer: Having spoken with several friends who received interviews during the international round in the past couple of years, it seems there has been a range of notification dates from the last week of February to the first week of March. Last year, for example, a friend heard about his interview offer on March 4th. The Gates website lists the following information as well:
Applications open
4 September 2017
Application deadline
Dependent on your course - either 6 December 2017 or 4 January 2018*
Departmental ranking
December - February
Trust shortlisting
Early March
Shortlisted candidates invited to interview
Early March
Interviews
27 & 28 March 2018 (Cambridge, UK)
Scholarships offered
Late March
Scholarships accepted
48 hours after offer