How long does it take to close the gap after having 2 upper premolar teeth extracted? I also have braces?

Avg. 6 months-1 year. There is no exact timeframe. Every situation is different. In adults, it usually will take longer than in children/teenagers. Teeth can be moved very quickly, but past history shows that long-term problems can occur if teeth are moved too quickly. A good orthodontist will have a game plan for your whole orthodontic treatment plan and will unlikely close the upper premolar spaces too quickly.
Depends. Closing the space created by the extractions is only part of the picture. As the teeth are pulled together, they can rotate and/or lean either mesially or distally. Although the space may close, the teeth need to be uprighted.
Months. Depends on your cooperation. The better you follow your orthodontist's instructions, the sooner the space will close.
6+ months. A typical upper first premolar is 8-9mm in width, and modern materials and biomechanics can typically close 1.5mm per month (not just tipping, but crown and root), other spaces may open up and must be dealt with, and correction of the occlusal scheme depends upon the original presentation, so treatment is usually 18 months.
9-12 mos. Although the answer is highly dependent upon a large number of different factors (amount of space, rate of your metabolism, compliance, biomechanics employed, etc.), a reasonable estimate would be 9-12 months to completely close the space. However, that does not mean treatment is complete! there may be many other issues that also need to be addressed before you are finished.