Again, my GUI I/F's takes 2-3 weeks or more typically a month to plan out how they work. A few days or even a week to code the plan is not that significant. The 2 weeks to a month deciding how it will work is the most "design effort" and that part is hard. You just will not come up with a good GUI, if you "slap things together" - the planning part is the most part. The implementation part is the least part.