There are no perfect times to come here to study as much depends on your personal preferences for hotte colder etc. and the wider weather patterns that year.
Generally for most people staying 2-3 month reliable periods are the Spring and Autumn and one can ma personal choice to start earlier or later depending on whether you don’t mind a little cold weather or hot weather.
At the same time many people love the Summer here and don’t mind or enjoy hot weather and so this can good time to study using the early mornings and early evening for Tai Chi and leaving the daytime free for enjoying Yangshuo’s surrounding scenery, caves,water activites etc.
The other factor to take into account is that during ‘lower’ seasons,when the school may be less busy, they more chance of getting individual tuition with the teachers.
Finally everyone has to consider influences from their home situation.
The main thing is that you are able to learn Tai Chi well when you come and school’s covered areas have dealt with the most difficult problem limiting study which was wet weather.