I'd try to get him to learn them but I wouldn't go overboard unless you're set on him getting a career as a bartender!
Kids don't do maths at primary school they do arithmetic and when they start to do maths at secondary school their tables and arithmatic tends to drop off a bit anyway so starting with a good base now is good.
An hour a night seems a little heavy for learning parrot tables parrot fashion - why don't you do half an hour tables and half an hour maths starting some of the things like basic algebra and trigonometry.
It's amazing how many people got turned off maths by being forced to chant tables.
If you can instill in him a genuine enthusiasm and sense of fun in a subject like maths it's worth more than knowing that six sevens are fourty two.
Incidently this years Royal institution Christmas lectures are on maths.
http://www.rigb.org/rimain/events/christmaslec tures.jsp
I think they're fully booked now but they're really worth watching over Christmas