Create a splitscreen video from two videos of different lengths with delay
Get some basic knowledge of premiere Pro first. 


Import both videos and set the settings for your output. 
Move the right video in the timeline to where it should start.
Use effects to slow down or speedup your video
Create a still of the first frame and add it to the layer. You can do this as easily as a screenshot and cut it out with photoshop. Ah hell even import the video to Photoshop.