Congrats on getting decision made! Timing really depends. Some get oath quickly after DM. Others wait months. It's really hard to predict when you'll receive oath, but hopefully in the next couple of months!
What city did you apply from? Or what office is processing your application?
What it a single application or a family application?
Your application was delivered on Jan 18, 2021? What day did you mail it?
What is your in process date on ECAS? (I suspect it is around May 30, as it is normally several days before the background check is completed).
What date did you first receive your test invite?
Thanks for the info so I can add your info to the tracker