No. I've done my share of stupid/risky things, but I'm simply not going to work on a side business while actually in the office at my day job.
That said, I used to know someone who did exactly this successfully. However, while he was an engineer, his day job had absolutely nothing to do with software development and gave him lots of free time "at work" when he would just have been bored.
The way I see it for me there are four outcomes:
1) Company discovers and I am fired.
2) Company discovers and has no interest.
3) No one finds out and I have decent side income.
4) The app has good success and I quit one day with a phony excuse before they become aware of it.
In my case, 1/4 is actually bad but the likelihood of discovery is low because my company is not in that field. I'm not likely to be fired without warning and it's not likely to be discovered while the app is transitioning from side income to success (before I can leave, if the app is worthwhile to litigate over).
Worst case is company discovers, fires you, and takes all rights to the code. The IP belongs to them and you have to decide if it's worth the legal risk of continuing to develop it commercially. Hint: it's generally not.
It's easier to avoid this problem than deal with it after the fact.
That said, I used to know someone who did exactly this successfully. However, while he was an engineer, his day job had absolutely nothing to do with software development and gave him lots of free time "at work" when he would just have been bored.