Hi folks... I'm hoping for some advice from more experienced home developers - well, more experienced than me, which probably means most of you good folks!
I started shooting and home-developing black and white negative film late last year, though I haven't done a great deal of it yet (only half a dozen rolls or so). I've been shooting mostly Fomapan 200 at box speed, developing with a spiral tank in Fomadon R09 (~ "Rodinal") 1+50 @ approximately 20 deg C room temperature - using Massive Dev Chart timings (10 mins) and agitation (gentle inversions) - and achieving generally satisfactory - dare I say pleasing - results.
With the alarming increases in energy pricing here in the UK, I'm now maintaining the average temperature in my home closer to 18 deg C rather than 20 (it felt rather cool at first, but my family and I are used to it now

). I haven't yet developed any film since making this change, and I'd like to give myself the best chance of success when I do, using solution that's stabilised at room temperature.
For the first time, I've just looked at Massive Dev Chart's "Time/Temp Converter" tool and Ilford's Time/Temp Chart. Apparently, my 10 minutes development time at 20 deg C will increase to a little over 12 minutes at 18 deg C... but I'm drawn to MDC's warning:
"
These conversions are approximate and are based on standard black and white film in normal developer. Films and developers vary widely so you should always test any time/temp combination prior to using it on important work"
None of my "work" is especially important - it's all hobby stuff purely for my own enjoyment and learning, and failure isn't a big deal - but obviously I prefer to succeed
So... after that long pre-amble... my questions to you more-experienced film developers are as follows:
1) Should developing at 18 deg C pose any significant problems?
2) How reliable do you find the timings in Massive Dev Chart's Time / Temp Converter tool?
3) Has anyone used the same combination of film stock - Fomapan 200 - and developer - Rodinal - at lower than 20 deg C, and if so, at what dilution / timing / agitation?
Many thanks in advance for any advice, opinions or thoughts on this - and apologies for any newbie errors (choice of forum, terminology etc.) in the above