I just spent a couple of hours doing some testing of dialogue replacement.
Can you say "tedious"?
I thought you could.
Now say it over and over for about two hours, or until your ass starts to hurt because of the uncomfortable chair.
After that, assume that you have about 30 seconds of running time done. And that's just the dialogue, that doesn't involve any actual processing, or adding sound effects, or foley work. Figure around six hours of process per finished minute.
Then realize it's a 70-minute movie, and figure somewhere around half to 2/3 needs that level of work. And that's just the sound. There's still the scene-by-scene (actually shot-by-shot) correction that needs to happen. And digital effects.
Let's say around 500 hours.
Let's say I can do a 20-hour week. That's a heavy load. That's also 25 weeks.
First order estimate of the postproduction is around six months under the assumption that I could devote the equivalent of a part-time job to it. And knowing that I have to have the front porch finished framing by the end of April, 'taint gonna happen like that.
So now, to backfill: assume that I have three weeks to record all of the actors for the dialogue replacement and get a first cut done. Assume it will take a week just for the recording.