Commonly speaking, the factors below would affect the conversion time.
1. The size of video. The larger video usually means longer conversion time.
2 .The output quality setting. The higher quality for the output file, the longer it takes. It is suggested to select Format>Common video instead of HD movies. Meanwhile, click Option next to Format to enter the dialog, lower the parameter of Resolution and Bit rate accordingly.
3. The hardware configuration of your Mac.
4. External environment during conversion. If there are many other programs are running at the same time with the conversion and occupy the CPU resource too much, it will also affect conversion speed very much.