I would probably expect it to take effect over weeks and months rather than instantly.
I've got several weeks coming up with 4 hours of train travel every day, so I feel I'll have a pretty good idea by the end of that!
I would probably expect it to take effect over weeks and months rather than instantly.
I've got several weeks coming up with 4 hours of train travel every day, so I feel I'll have a pretty good idea by the end of that!