Drag the edge of the interval, where it breaks, to the end of each 50 minute segment that will give you two 50 minute intervals.
So for the first one the end of the 18:53 interval drag it to the end of the 50 minutes (around 1 hour 10 at a guess)
The mouse pointer changes to an arrow when you grab the edge. Hold down your mouse key and pull/scroll to the right.
Edit: It has split the intervals because you reduced power enough for it to detect and consider it the end of the interval, stopped pedalling or it lost cadence readings for some reason.
If you struggle to use your mouse to edit the intervals you can change the interval in the table, see screen shot
Personally I find it easier to use the mouse.