No there is no good seaonal time for a big cut on prices for a bike. That said, there are sporadic sales and Trek hacked the prices on the ALR Emonda by $300 bucks. That was Trek's, not the LBS, doing.
What you can do to compensate is go in with a list of things you would like a discount on alongside the bike. The margins on the bike itself are very low. Get your bike picked out, and tell the salesman that you need some accessories. Helmets are often marked up by 50% if they are the store brand. Saddlebags, tubes are at least 25% off. Shoes and clothing, for some reason, might be only discountable by 10%. Don't forget the waterbottle cages (ask for buy one get one). And on the way out, see if they'll throw in two LBS branded water bottles.
And before I get hated on, I worked at a LBS for 5 years. Mechanic (mostly) and sales. These things are viewed as an investment in you coming back to the shop and buying other goods, especially service on a bike. Furthermore, your gushing words of praise are bought cheaply for those discounts that didn't cost the LBS profit as they did not go below margin. It is essentially an investment of forgone profit into future business.