It will mostly come by email if you have provided them with an email address. After DM, it depends when you applied. Right now, they are doing June applicants for oath at Scarborough. If you are with Scarborough and applied in June, then any time now (may be in few days or within a week) you will get your oath time.
Myself, I am a July applicant and I have been a Decision Made for almost close to a month. And some are waiting for more than 3-4 months but oath call is coming by the time you applied; not the time when you took test.
This is applicable for Scarborough; at least.