How to aggregate data from a given figure in a given time interval?

Hello everyone i generate traffic for machine type communication and i have to compare some models, I want to work with an aggregate traffic model from 3GPP, i have attached here the figure, i already have the x and y values in a matrix. What i want to do is to aggregate the traffic in a given time interval. For that case it is a source model and all devices generate traffic in 1 hour , but what i want is to aggregate the data which is generated lets say between 0 and 400 seconds and show in the figure as its a single entity which is an aggregate data, Can anyone help me please?