Forum:(MGS:PW) R&D Question(s)

I have a curiouse question about the R&D area for MGS:PW. When researching and developing weapons and items, you have the option to reasearch multiple items at once. In doing this, does this mean that the production of these multiple items take longer than if you were to research one item at a time? Or is there a set time to how long it will take before production for each item is completed?