Apologies if this is a bit of a newbie question.

Im travelling in August and have been watching fligth prices for a month or so from EDI to SEA and they seem to fluctuate daily and even throughout the day.

Will be flying with KLM/NWA via AMS or Air France via CDG by the the look of it.

The only reason I have not yet booked is only today Ive had confirmation of dates/holidays and I'm waiting on my new credit card arriving (today hopefully).

Is there a best time of day to book flights?
Is there a best period to book flights, say 2, 8 or 14 weeks in advance? - for example?
Any other last minute ways to save cash?

Looking on expedia and opodo - seem cheaper than any other sites ive seen.