Explanation needed on "stubble trimmer"?

Nearly feel ridiculous asking this question at the age of 32, but up until now I have always shaved with a razor blade for a full clean shave but now am looking to buy an electric razor to maintain that 2 Day stubble look.

I bought a "stubble shaver" last week with it`s lowest setting being 0.5mm in length. I thought on buying this that a grade of 0.5mm was super low and that I wouldn`t even have to go that low to get the 2 day look I was after. I deliberately hadn`t shaved in 6 days in anticipation of using my new electric shaver but on using it, I realised that even using it`s lowest setting at 0.5mm, it didn`t as much as take a whisker off my face. Now I realise that everyone grows facial hair at different lengths so before you think that my facial hair wasn`t long enough at the time of trying out the new shaver, I can assure you it was decently grown in that 6 day period, certainly far beyond what a 2 day look would typically look like on any man.

I thought perhaps that I was using an incorrect or poor technique so researched this by reading the instructions, looking at tutorial videos online ect and repeating these. Regardless of how many times I tried and different methods of using the blade I tried, it still wouldn`t bring the facial hair lower than the 6 day hair growth I had.

So, question is: Does 0.5mm typically bring facial hair to that 2 day unshaven look or do I need a shorter blade? ie - 0.1mm?

Thanks