According to 9to5Mac:
Apple is currently aiming to unveil the new 4-inch the iPhone 5se, the iPad Air 3, and new Apple Watch band options at an event on Tuesday, March 15th, according to sources. We previously reported that Apple was on track to launch the new products during the week of March 14th. As the scheduled event is still a month-and-a-half away, the date could conceivably still shift or turn into an online announcement.
It was previously reported that Apple was targeting the launch of these products for this particular week in March. The company held an event last March to introduce a new products, including the 12-inch Retina MacBook, so it would make sense for them to hold one around the same time this year if new products are ready to go.