Your board can take up to 10-15 minutes of continuous pumping to fully inflate. 

This will vary depending on how quickly you pump.

It is a good idea to begin pumping with the pump in dual action mode and once the strokes get harder, remember to switch to single action. We recommend pumping the board in 4 sets of 3-minute pumping, to allow yourself some rest.

An electric pump will certainly take the physical element out of pumping up your board, but it's important to note that it will not necessarily make it much faster.

See also: 

How Do I Inflate my Board

Using a Manual Pump 

My pump pressure gauge is not working - what do I do?