The Russian space, personnel explained that this lengthened space trip is meant to study and analyze the new tech on board. The unmanned probe is also designed quite different from the manned craft. It is also divided into three ships, but the crew compartment has been redesigned to carry fuel. This modification allows it to travel for longer, and has facilitated the two-day trip effectively.
"The two-day rendezvous for Progress is deliberately planned to enable Russian flight controllers to test new software and communications equipment for the new vehicle configuration that will be standard for future Progress and piloted Soyuz spacecraft," NASA said in a statement. "[It's] a flawless ascent to orbit for the Progress resupply vehicle, the second in as many weeks to head to the International Space Station, with a third resupply ship, the SpaceX Dragon cargo craft, scheduled for launch on April 8,"
This is indeed an exciting time for space science. This is the third launch to the International Space Station in 21 days. All the previous two have been used to send supplies as well. Next week SpaceX will also carry supplies to the space station. The company is also looking to test their new compressed oxygen fuel.