I am looking to concat a video and an image using ffmpeg and was wondering if when cutting the video I can cut it with a timecode that uses seconds:frames (00:00:23:4)instead of seconds.miliseconds (00:00:23.43) and then concat it with seconds:frames?
No, see the time duration syntax documentation for accepted syntax.
You can use the reciprocal of the output frame rate instead. For example, frame #5 for a constant output frame rate of 25 is 5*(1/25)=0.2.