Thought I'd give Gardengal a break ha ha.Yes you can overwater any maple in any potting medium.I've killed more than I care to mention by doing so.Even a soil-less,super free draining mix can retain too much water within.
I know,you see shrivelled leaves,you panic and you add more water....done this too many times in past.
It's always better if in doubt to underwater than overwater.If there's a little water present the maple's not gonna die but too much water can kill it.
Always check first,use the finger test as GG suggests,get to know the weight of the pot when quite dry and freshly watered.Barbeque wooden skewers are great for gauging the moisture in the pot.Leave them in there and withdraw when you wish to water.If they're already moist all the way up then don't water....even if the leaves are crisped.. you can't repair them but don't add more water.The plant will look fine again next year but at least it won't be dead.If skewers are dry at the top 2" and damp as you go down then you can water a little,you can feel where the water is.If the skewers feel actually wet anywhere except right near the bottom of the pot then don't water,there's already too much.
It sounds hard I know but necessary,remember containerising plants is always a compromise,you have to do a bit of work.
I'm in UK(Kent) too,to emphasise my point,some of my newest maples are still in their original potting medium and can need watering every day when weather's nice.You can feel the pots are light,the plants have 'drunk' all the water and start to wilt very slightly...obviously these one's aren't retaining much water but are healthy,the slight lack of enough water is doing no harm..it's just a bit more work.
Good luck..don't panic...and DON'T OVERWATER :)

Well said, houzi :-)

Well that's at least two of us in Kent, I know lots about Dahlias but probably nuff all about JM, but as houzi said, maybe feel the soil in the container first and see if its moist, also keep the JM out of the wind as this can dry out any plant very quickly.....I was thinking of buying a moisture meter a few months ago.........but your fingers dipped in the soil for a couple of seconds will probably do the same thing..