Well, if you left the car over the winter without any protection, you
have at least gunked your fuel filter up and maybe even the injectors.
If you've got fuel that's been sitting for six months, it's got all
kinds of varnish precipitating out of it and even the high pressure BMW
system which is almost immune to clogging can fail.

Your battery is probably on its way out, too.

If it were my car, I'd change the fuel filter before doing anything
else, and I'd run a couple tanks of gas with a lot of injector
cleaner in it.  I'd check the fuel pressure at the rail next.

When you changed the plugs, what did they look like?

Next year, put fuel stabilizer in the tank, and run the engine to get
the stabilized fuel everywhere through the system.  Pull the plugs and
squirt a little WD-40 in each cylinder, and disconnect the battery.  
Put the battery on a float-charger if possible.  When the time comes to
restart in the spring, check the battery condition, and turn it over
without the plugs to get the WD-40 residue out of there before starting
the first time.
--scott

If you turn the key and it starts within about 5 seconds, it is normal. You
should not be concerned that it once started in a second, and now it takes
3. You will drive yourself to drink chasing this kind of problem.

2 months shouldn't matter, so don't worry about it. Use up the old fuel
and see if things improve after a refill. Don't bother replacing
anything because of this, other than normal service of course. It
usually takes longer to start in cold weather too.

Ulf