I am not sure about the arrhythmia part, however after spending 15 years in the fitness industry most fitness pro's say the morning is the most effective time to exercise.
Morning or evening. I think if you are young either time if fine, pick the time that it you're most likely to "keep"...i.e., actually exercise.
If you're older (I'll not give a number, it all depends) then you may be too tired to do a good exercise session in the evening...that's been my case for a number of years. In fact I prefer noon time, so I'm a neither.
If I'm going to go to the gym, it has to be before noon because I slow down after 3 pm. I can go and go, running around from 6am to 3pm and then it feels like someone pulled the batteries out of me. Plop.
I agree with Jerry - whatever time works best for you in terms of free time and energy, go with that. In any case, be sure to warm up before you do the heavy workouts. Don't toss on the sweats at 6am and go out for a jog.
Thnx for the posts. I have NSVT and have been doing a bit of exercise- fairly intense table tennis, which seems to suit me better than a half hour walk- in the evenings. Now I plan to play in the early morning, and wanted to know if it was more risky. The posts have been of great help. Thnx again and with best wishes,