I intend to travel to Europe for a Euro trip. I'm planning to apply for the Schengen Visa now (March) and intend to travel to Prague (first point of entry) in May for 8 days (and that is the itinerary I will provide to the Embassy which will give my planned visit and tours for May). However, there is a possibility that rather than go in May (as I initially plan) I may need to change travel dates to July and go on the tour then. So assuming my visa is issued by April and I am not able to go in May, can I use the Visa for traveling at the end of July? Basically, will the visa still be valid?
Maybe, but probably not. You may be able to increase the chance that it will be by indicating in your application that you may want to change your dates from May to July.
Schengen visas have two time limits: a validity period and a "duration of stay," which is a limitation on the number of days the bearer can spend in the Schengen area. If you submit an 8-day itinerary in May, you will likely get an 8-day duration of stay with a validity period that should be only slightly longer than that. If you tell the consulate that there's a good chance your plans will change, they might issue a visa with an 8-day duration of stay and a validity period that extends from May to July.
Be careful with day counting, though. If you plan to arrive on a Saturday, for example, and leave on the following Sunday, that is nine days, not eight, because you must count every calendar day in which you spend any time inside the Schengen area. In other words, you must count the arrival and departure days, regardless of whether your time of departure is before or after your time of arrival. We've had at least one question on this site from someone who miscounted his days on his application, and the consulate did not correct his mistake, so he got a visa that wasn't actually sufficient for the itinerary he had submitted.