Joint tenants (Unity of Time) question

[Maxym Le Deux]

Hello everyone. 

My wife and I would like to purchase property from our landlord and become Joint tenants (me, wife, landlord). I'm looking to understand the "Time" aspect in Joint tenant qualification. We all live in the same house and would like to own it. We are doing owner finance and would like to avoid property reassessment. Under joint tenants, it does not get reassessed however I don't know if it's possible to do a "transfer" or "Add"  our names to the title so the property becomes Joint tenant instead of Sole ownership. 

I'm really confused on "Unity of time: The interest of the owners is acquired at the same time." Does this mean since the landlord is the owner this point will not be satisfied anymore?