The time aspect of music is also the part that is more difficult to teach. Notes and chords and rules can be learned, but you either have a sense of rhythm or you don't. Fortunately, those born without this gift usually have no interest in music. The fact that you've come to this page site shows that you must have this sense of rhythm and time. Strumming Do me a favor .
Metronomes are a good way to practice playing in time.
There are many electronic versions availble these days. Better still are drum machines. They can be easily programmed to play any rhythm you can imagine and playing along with them will train you ear and hands to keep good time. Also, programming them will give you a very good understanding of how featureless time can be intricately divided and turned into music.