Sorry to ask a query I should know the answer to, but I have not been traveling UA much for a while.
I am still an Elite (Old Flex PQP got me here)

I am due to leave LHR on Friday at 8 AM (60k UA award no longer offered)
My plans have changed and I will have to get up way early at Stroud in Gloucestershire to make it to 8A flight

The current prices are 180k or more in C for same day later flights at noon and 4 pm. I cannot even get an economy ticket for 60k
So I do NOT want to change the award ticket now

Q1
Can I SDC to later flight - 12 noon on Thu for 12n flight on Fri and 4 pm Thu for 4pm flight on Fri?
Of course I know there may not be space but in general at +24h do they care about fare classes for saver awards or is it just a SDC ?
Q2
Is my updated UA app on my phone sufficient ? or do I need my laptop there?
I am trying to go light and not lug too much luggage in the wilds of the Cotswolds.
Q3
Is my best bet to change my trip plans and make it to near LHR the previous night?
Anyone with experience in schlepping to LHR from the western wilds please let me know

Thanks