How long will it take to learn Welsh? Do you have any tips?
It depends on your learning style, your effort, your time and the amount of immersion you use. Also, use other apps with it. Go for quality of language and don't worry about the length it will take you - push yourself but review also. Once in a while, take a break, but don't let it be long (and you can always just watch a Welsh cartoon or something on youtube on your 'break day' to keep it fresh in mind). :)
It depends on to what level you want to learn it. If you live in Wales then you should also join a local Cymraeg i Oedolion (Welsh for Adults) course, and try and spend time in Welsh-speaking places when you have a chance. The on-line course 'Say Something In Welsh' is also well worth following, and will introduce you to some more informal language patterns, too.
Do whatever you can to extend your vocabulary. There are several vocab learning systems such as 'Memrise' around, and many sources of flash-cards to work with. Try to look up and learn genders and plurals as you go - many flash-cards leave those out, so you may need to add them in yourself.