I completed a Cambridge CELTA (Certificate for English Language Teaching to Adults) last June. Basically the same as TESOL, TEFL etc etc. I did it part time over 6 months. It was full on, and I can only imagine how it must take over your life if you do it full time. We taught every week, real students, always observed (by our tutors and fellow students) and assessed. It was stressful, esp at the beginning, but very rewarding

when a lesson went well. The biggest element, in terms of time committment, was lesson preparation. I could easily spend 5 hours preparing for a 30 min teaching slot. My fellow students found it the same. There were also several written assignments due over the duration of the course which counted towards the final mark.
It was interesting, challenging, rewarding and sometimes scary

. I would say go for it, but be aware that it is not a walk in the park, it is hard work. Out of a class of 9 to start with, 6 completed (and all passed I think?!). Three withdrew, one due to family bereavement, the other 2 because of the pressure.
Of course, doing it online might make it quite a different experience.
SM