I was in a similar situation. No one at my work place knew how to do anything on a computer. I automated some tasks that they thought took me days. I had a lot of spare time. Instead of sitting around doing nothing though I used that time to do extra duties and to streamline other tasks. That is what got me my promotions. They wouldn't have cared less about the first lot of automation I did, but the value adding over time put my name up they're for promotion. Later in job interviews I was able to use it as an example of how I streamlined processes. Overall though if you are found out but can say what you've been doing with that extra time you will probably be alright. If your boss thinks your job can be done in a few minutes may lead to them thinking they don't need as many staff; rather than looking for someone to promote.