best time to buy delta airlines tickets

Prices vary but the closer to peak times the more expensive plane tickets get. If you want to fly on Delta airlines from BOS to Finland, you can probably find some very good deals in February. On the other hand, that is one of the most expensive months to go from BOS to Florida.

The best fare for delta flights for travel on a given day can occur at any time. The talk about 45 days out, or purchasing Wednesday at 12 am just after midnight, or never buy tickets on the weekend are all myths. I've seen the best fares offered at 331 days out in some cases and 30 days in advance in others. The best way to secure a good fare is to start looking 331 days in advance of your travel date and check everyday (several times a day, if possible). Knowing what the "standard" rates are for a route allows you to jump on a good fare when it appears.

If you are booking closer in and unfamiliar with prices on a route, it is more difficult to ascertain a good fare from an ordinary one. One trick is to check what the fare would be if you booked travel for 331 days out. Forget for the moment that it is not when you want to travel. It will give you a good idea of what the "standard" fare is. If the fare for your travel date is the same as the 331 day fare, it's very likely that you should wait. If the fare for your travel date is higher, you probably already missed the good fares.
The "high season" for a particular location is often decided by its weather.

Also, holidays have to be taken into consideration. Flying right before Christmas is usually more expensive than a few weeks later. If the children are out of school, trips anywhere tend to be expensive -- but more so if you are talking about Orlando during the Christmas or Easter breaks.

Also, unless you are a major football fan, I would strongly suggest avoiding a city on the weekend that it is hosting the Superbowl.
Also, check the delta airlines website homepage regularly, as they sometimes announce one day sales to cities in Europe. I have heard of some amazing deals to london in the $600 range for June/July.