1.I think he may read the clock/watch wrongly.
2.I read the clock/watch wrongly when I went out in the morning.I started 20 minutes early/late.
3.I think you recognized the person wrongly,This one just looks like the person you are looking for.
4.My watch is 20 minutes faster/slower
5.She used to make the watch 10 minutes faster/slower (early/late).