Quick turnaround on a beer for repitch

Ingredients
1

I generally leave all my beers in primary for at least 2 weeks by default, but I have a 70/- that I brewed last Tuesday that I need to get off the yeast after only 8 days. I’m using it to grow up a pitch for a Wee Heavy, and Wednesday is my only possible brew day for the rest of the year, and probably well into January.

Here’s some more details:

I underestimated the boiloff a bit from the side boil and 120 minute main boil and ended up with 2.5 gallons at 1.042. I pitched 1 vial of WLP028 at 58F, then moved it to the 60F ambient section of my basement. It ramped itself up to 64F and had a thick krausen in less than 24 hours. After about 2.5 days I moved it to my 66F ambient section of my basement and it’s been around 68F.

So I’m trying to figure out my best option. I’ve never used this yeast, but given it’s vigorous fermentation at such a low temp, I’m thinking there’s a good chance it might be done with a 1.042 beer within 8 days. But I have no way to flush a secondary with CO2, so I hate to assume it’s going to be done only to find I need to give it more time at the last minute. If I think I’m going to need a secondary I’d prefer to rack while there’s still a few points left so the last bit of fermentation can help purge the carboy.

So, does anyone have any thoughts on what my best plan of action is? Does anyone with experience with WLP028 know if it’s likely to be finished with a beer of this gravity in a week?

I’m thinking of taking hydro samples the next 2 days. If it’s done then I’m good. If it’s not, then I’ll rack it Monday night and bring it upstairs to warm up so some CO2 will come out of solution and help purge the carboy. If it’s close to being done, then I’ll bring it upstairs in the primary to try to get it to finish out.

2

I would let it run its course. The yeast will survive till your next brew day.

3

If purging a secondary with CO2 is your preferred option, you can generate your own CO2 with a small starter fitted with tubing to direct the gas into the secondary vessel. You can just ferment cheap cane sugar with whatever yeast you have on hand since the only purpose is to produce CO2.

4

O28 is  solid fermenter, so I’d be surprised if it needed more that 7-8 days to finish a 42 point beer.
Maybe for insurance purposes, warm it up to the low 70’s for a couple of days.
But as you suggest, do a couple of gravity checks to be sure.

5

That strain will work fine down into the 50s, so I am not surprised it went fast at 64F.