The duration of generate trans video

[shudct]

/usr/bin/ffmpeg -y -loglevel warning -loop 1 -t 1.5 -i end.png -loop 1 -t 1.5 -i start.png -t 1.5 -i blank.wav -filter_complex gltransition=duration=1.3:offset=0.1:source=LinearBlur.glsl -ac 2 -ar 44100 -b:v 2M -r 24 -pix_fmt yuv420p -strict -2 -preset superfast transition.mp4

I used the code above to generate a transition video(1.5s), however, the ouput video is 1.58s. Is there anything wrong? Please give me some advice to solve this problem, thanks~