Faking Dusk in EXT. overcast daylight conditions

[Aidan Brook]

Hi guys ! 

Just looking for some advice on an upcoming student film I'm shooting. It's an 8 page script, that all takes place outside a community hall during late afternoon/dusk. It's a single conversation, all in real time. We have the budget for a 2-3 day shoot, and the director is very adamant on shooting during dusk/close to blue hour, however the producer made it clear that's unrealistic, due to lack of time. 

So, it's my job to try and fake the look during the day. How do DoPs usually deal with shooting a long EXT. sequence like this, that doesn't involve scheduling for the 1hr of correct light everyday?  Luckily, where we're shooting in the UK it's often overcast, providing a nice, soft source which is what we want. I'm just worried about the colour being convincing, as I don't want to leave it to the colourist. I was just wondering if anyone had any advice for dealing with this situation? I just want to make sure skin tones look accurate, and not washed with a blue tint in the grade.

My other worry is if the weather is different across the 3 days, as we won't have much equipment other than some frames of diffusion to soften sunlight. 

I wasn't sure whether altering the white balance throughout the day would be worthwhile, as I imagine matching shots in the grade would take forever and not look great. Also thinking about using a blue filter to try and get the look. 

I plan on shaping the light using Poly and Neg.

Please see some reference stills below.

Any advice will be much appreciated !