My concern would not be with the fact that you're going for lunch earlier than most, but with the fact that you said "exact 2 pm".
My experience, in a programming world, is that if you leave your desk at the exact same time (lunch or evening) every day then you get a reputation for it. And it's not entirely unfair. This is not the kind of job where you can finish a task at an expected time so, if you're leaving at the same time then the assumption is that you're spending the end of each morning/afternoon clock-watching.
That said, it is culture-specific. I have worked for one company where that was the norm. The end of the day was 5:15, which was deliberately specific, and everyone shot up and left at that time. I didn't (largely cause I didn't then want to spend an hour getting out of the car park) but, because that was the culture, I didn't get credited for it. If I was ten minutes late in the morning, I was in trouble and, if I finished a task at 5:10 one day, I couldn't make the adult decision to leave early "just this once".
Since then, I've deliberately looked for companies that have a more flexible time-keeping culture (especially in London, where missing rush-hour makes for a much less stressful day). But, in those, I've seen the people who do follow a strict and inflexible pattern frowned upon harder than others who don't even do their standard hours in a day (assuming they mostly get the job done, nonetheless).
But, I will stress that this answer is because you asked about the etiquette side specifically. Fact is that you won't ever end up getting fired for working to rule.