If you mean that playing 1 minute of video in Shotcut actually takes 1 minute and 7 seconds, it’s probably just the Player that is lagging. This can happen for many reasons: Like working on a project with many tracks/clips/cuts, or using filters that use a lot of resources. Using heavy video files (like 4k, 60 fps) on a computer that doesn’t meet the requirements for these files will also cause lagging.
One thing you can try is to go to Settings > Player, enable Realtime (frames dropping), and see if that helps.
Using Proxy Editing and Preview Scaling will also help.