Delaying video overlay in ffmpeg without frame drops
Try

ffmpeg -framerate 60 -loop 1 -i ~/Desktop/FP2.tiff -i ~/Desktop/fp.mov -i ~/Desktop/fp.mov \
       -lavfi "[0][1:v]overlay=10:(main_h-overlay_h)/2:format=rgb:shortest=1[v1]; \
               [2:v]setpts=(PTS-STARTPTS)+2/TB[2v]; \
               [v1][2v]overlay=460:(main_h-overlay_h)/2:shortest=1:format=rgb[final]; \
               [2:a]adelay=2000|2000[a2];[1:a][a2]amix=inputs=2[audio]" \
 -map "[final]" -map [audio] -c:v ffv1 -level 3 -c:a pcm_s16be ~/Desktop/filtergraph.nut


If this still drops frames, then you should insert a FIFO filter for the 2nd video after the setpts, like this:

[2:v]setpts=(PTS-STARTPTS)+2/TB,fifo[2v]