> No they don't know and if they did I would get fired obviously.

This already shows the problem. They assume they are paying for your time exclusively, while you are doing just enough to satisfy them.

The fact you go such lengths to hide the fact that you are three timing them also shows that you know what you are doing is not acceptable.

Most likely you are in breach of the employment contract.

You are also somehow justifying this to yourself. The problem is that such behavior causes loss of trust and makes other 95% of honest peoples' life painful.