Bad-faith N12: what's the time-frame in which the landlord must move in?

Long story, but my next door neighbours live in a side-split duplex. It was purchased last spring by an out-of-town investor who immediately offered both tenants $4,000 cash-for-keys. The one tenant, a single woman, accepted. My other neighbours, a young couple with a toddler, turned it down. The LL then tried jacking the rent illegally by a quite substantial amount and was told to kick rocks. The empty unit was listed briefly by a,management company last summer but has remained vacant these past 18 months.

Over the past few weeks the LL has had people in the empty unit doing upgrades. The wife has verbally informed my neighbours they'll be issuing an N12, but nothing officially yet. Due to a lot of circumstances, it's pretty obvious this'll be in bad faith.

Let's say the LL is eventually successful in uprooting my friends. We already know the conditions on who they can move in and for how long, and that if the other unit is still available it must be offered at the same rental rate. My question is this, and I've done some sleuthing without any results: once my friends vacate their unit, what's the time-frame in which the new occupants must move in? The duplex where I live sold around the same time and the new owners N12ed the fellow upstairs. They took some time doing renovations before they eventually moved in almost 12 weeks later, and at the time I heard that the window of unoccupancy was 90 days, but I haven't found that in any of the regulations.