I am looking to finish off my leftover ingredients and can just about make a pale ale with OG ~1.04 or so. I'd like to get it started tomorrow, but I probably won't be able to rack it until the first or second week in January. Will it be OK in the primary for 5-6 weeks or should I wait until after the New Year to do it?
I've had off flavours creep into several beers that were 4 weeks or longer in primary. If you can crash cool it (after a couple of weeks) until you're ready to rack then that will reduce changes of off flavours and you'll also end up with a clearer beer since the yeast will drop out more efficiently.
leaving the wort on the primary yeast cake for over 3 weeks is not advisable. The yeast begin breaking down their waste products, better to transfer wort off the primary yeast cake into a secondary to continue the conditioning phase. Watch out for those Diactels, you'll get some real off flavors.