For this I'm going to presume that your work has a communal clock and you own a watch.
Step 1: Make your watch late.
At the start make it around 5 minutes late.
Step 2: Make your work clock fast.
around 10-15 minutes fast.
Step 3: Make people know the clock is wrong.
Start conversations about how the clock is wrong. You want to get people to not trust the clock.
Step 4: Leave when the clock says you can.
The clock says it's home time, so it's home time.
Step 5: Rock up late.
If someone questions you, rememind them the clock is wrong and that your watch is right. You'll be there just in time. This will work for a while you rocking up late and leaving early with out any problems but soon enough some one will change it back.
Step 6: Rock up late any way.
And tell them the clock is fast. Your watch says your on time so your on time.
Step 7: Stop before you get in trouble.
Show up on time for a little while then repeat the same process. Your co-workers will already know its a dodgy clock so they're going to fall for it again.
I used this trick all the time at my last job. My current job, no one has a clock or watch so it's even easyer to rock up late. The trick is to stick to your guns. The clock is wrong, your watch is right!
