Help w/ my process of reusing yeast

Plan on brewing a 1.080 old ale this weekend and fermenting with a portion of the yeast cake from a 1.040 blonde ale.
The blonde will be at 2 weeks in primary at the time of all this.

If I understand the Mr. Malty calculator correct it's telling me to use around 140 ml of repitched slurry for the old ale. I assume this would be the volume of the yeast cake to be used, if not do I need 4x that amount since only about 25% of the mass in a yeast cake is actual yeast solids?

Now onto procedure:
My plan is to pour the amount directly from the fermenter or scoop out with a sanitized spoon into a sanitized measuring cup up to the 5 oz. mark, clean and sanitize the fermenter and pitch onto the new aerated wort. This will all be done within 30-60 minutes after transferring the blonde ale to secondary.

I was originally planning on just dumping onto the whole yeast cake, but further reading leads me to wanting to do it the correct way, but also the easiest way as I've never done this before.

the mr malty calculator assumes the slurry -- yes slurry being the yeast + solids -- will be fairly compact, like if you swirled up everything in the bottom after racking the beer, put it in the fridge and decanted after two days. but there is a setting to adjust this, take the slider towards "thin slurry" - like probably all the way. so i'd plan on using more like 300 ml of slurry.

i've had nothing but great success pitching slurry when i know i am going to brew within a week or so of the last batch. i don't even wash the yeast in this case - i just store enough slurry in a mason jar

since you're doing this all the same day, if you rack well and use one measuring cup (8 oz) + a little bit more of fresh slurry, that should work awesome.

Thanks, looks like I'm going to go with around 12 oz. to be safe.

Still trying to plan out my procedure since I'll have a lot going on with chilling the wort of the old ale, removing the reusable yeast, getting my primary cleaned and ready, etc.......

Any idea on the typical volume of a 4% yeast cake using Nottingham?
Just curious how much is actually at the bottom of a bucket...

i'm guessing there will be like a quart and a half of trub at the bottom. so you'll be using like a third to a quarter of the old cake. usually i add about a quart of water, swirl it, and pour it in a sanitized gallon jug for settling. it fills that jug a little more than half way up.

I was going to transfer then harvest the yeast while the new brew was chilling, but now you got me thinking of transferring and taking the yeast while I'm mashing that way it's all ready to pitch a couple hours before I need it.
Any problems of keeping the reusable yeast in an uncovered sanitized measuring cup for an hour or two?