Can a time limit be set for blynk use, per hour

IS it possible to use the timer as a one shot,
I would like to set a stop time (45 mins) start , a button widget will start the timer, and the timer would switch a digital output pin for that time(45 mins).
Would a seprate void be needed on arduino using mills .

Not sure you would need the Timer widget.

When you press the button invoke SimpleTimer’s timeout function to send the off signal 45 minutes later.

With Blynk’s slider you can easily vary the 45 minute duration if required.

See http://playground.arduino.cc/Code/SimpleTimer

Blynk’s Timer widget is best suited to the automatic control of circuits at pre-set times each day rather than circuits that are manually controlled by a button (physical or virtual).

The TimeInput widget might be more useful for you if you don’t want to get too heavy in SimpleTimer.

You set the on and off times plus it has the benefit of being a scheduler for different days of the week etc.