On a whole, Warframe requires about 50 hours and more to complete all the missions. You just cannot afford to miss any mission sich they are key learning blocks in the process of knowledge and having fun with Warframe. Additionally, experience with the game will always help you ace it in a much better and well-timed way.  Once you understand the nitty-gritty of the game's system, you will give a lot more time to other activities in the game itself.