'After that' vs 'then'

[subhajit123]

Hi there, Can I use "after that' and "then" Interchangeably in the following sentences?

1- Hey John, first clean your room, then/after that complete your homework.

2- He was first trained as a secretary and then/after that he got a job.

3- Yesterday I went to the market, then/after that I returned home and started cooking for my parents.

 

[GoesStation]

Both wordings are possible, but they require different punctuation.

He was first trained as a secretary and then he got a job.

He was first trained as a secretary; after that, he got a job.