The climax of the episode happened on July 4th, hence the title of the episode. However, the episode showed Steve training for that specific mission for a week previously, Then again, the prologue where the previous OSI agent assigned to the mission being killed was probably days prior to when Oscar reassigned Steve. It's a tough call but I estimate that the events of that episode spans about 10 days.
Jaime's age was never specied except for the opening title but I don't consider it canon just like the Dusty Springfield version of the SMDM title. I got Steve's birthdate from an episode that showed his driver's license.