Hi Larry,
I write from the outskirts of TQY, 10 minutes from NTA» (Newton Abbott - next trains) at 0550 and 30-40 at 1700
Travelling regularly-ish (2-3 times a month) into the City, I often go from NTA due to previous experiences of poor connections to / from TQY.
Leaving at 0630 NTA gets me into the city, via walk to Lancaster Gate then to Bank by about 0950 if everything's on time. Bear in mind that once you lose a few minutes on the B&H▸ (Berks and Hants - railway line from Reading to Taunton via Westbury), you often lose paths into RDG‡(resolve) & PAD» (Paddington (London) - next trains), I'm regularly 15-20 late into PAD.
So, leaving the office at either 1515 or 1615 ish gets me to PAD for the 1606 or 1703, into TQY (driving from NTA) 1900 or 2000.
So, 0550 - 1900 gives me 5 - 5.5 hours in the office for a 13 hour day door to door. The 1st PAD (0630) offers cheaper Apexs▸ (Advanced Purchase Excursion (fare)) than 0730 from NTA usually, and you can often get the holy grail of working on the train - a table, whereas 0730 that starts at PNZ, forget it. The airlines are hopeless for working IMO▸ (in my opinion) (OK with an iPad, emails etc)
Reliability is usually excellent, usual caveats apply
So, yes it's feasible but it's a long old slog of a day and I could get more done by working locally.