I find all four sentences to be correct.
Student or Learner
1. I will be playing tennis at this time tomorrow.
2. I am going to play tennis at this time tomorrow.
3. This time next week we shall be visiting museums.
4. This time next week we are going to visit museums.
I am aware that sentences 1 and 2 are OK, but I would like to ask sentences 2 and 4 are OK or not. If not, I would like to ask if we can use 'this time tomorrow, at this time next week,...etc with 'simple future tense' or not.
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.
I wanted to mean that 1 and 3 are OK, but I am not sure about 2 & 4.Sorry for the typo.