I'm an expert C++ programmer. I work with the language since 2007 now. I'm also very familiar with Qt, and will probably be using SQLite for persistence, either with the Qt driver, if using Qt, or with the official C API, which I'm quite familiar with. I prefer working with C++11 and above, if possible, but I work with C++03 very well, too. I also have a similar application I made for myself, using C#, that I can show you.
The 30 day deliver time is an honest timeframe based on this other C# project, time I spent on other Qt projects, and hours per day that I can dedicate to your project. Knowing that it is probably larger than the other offers you may have received, I assure you I will be delivering a very high standard product, that I know you will love.
Looking forward to working with you.
Best regards,
Cássio Renan