Several hours? I think somewhat longer.. how about a lifetime?
Making difficult splits with larger aperture scopes are long term projects, waiting for that perfect night when the seeing is super, making sure the scope is fully thermally equilibrated, it's not something that just happens when you want it too.
A Rayleigh split in Kevin's 25 inch is 0.22" and that's only a 25% drop in brightness from the maximum. Twice the Rayleigh Criterion is a full contrast split, the first minima overlap, that's 0.44", such seeing is very rare..
My efforts in cooling my 13.1 inch are driven by my interests in splitting close doubles. I've managed a few under 0.5", most recently a 0.44" but they are projects..
Now we can see why the USAF test chart has some advantages! OK its got issues, but a horizontal and vertical measurement could be done in minutes.