Lisa will have been making a cake for two hours by five o’clock this afternoon.

[Alice Chu]

Hello, dear teachers.
Could you please tell me if my understanding is correct? Thank you very much.

1. (A) Lisa will make a cake at three o’clock this afternoon.
→The action will start at three o’clock this afternoon.
1. (B) Lisa will make a cake by three this afternoon.
→The action will start before three o’clock this afternoon.

2. Lisa will be making a cake at four o’clock this afternoon.
→The action will be in progress at four o’clock this afternoon.
We can’t use “by” in place of “at” here.


3. (A) Lisa will have been making a cake for two hours at five o’clock this afternoon.
→The action will have lasted (for) two hours at five o’clock this afternoon, and the action is temporary.
3. (B) Lisa will have been making a cake for two hours by five o’clock this afternoon.
→The action will have lasted (for) two hours until five o’clock this afternoon, and the action is temporary.

4. (A) Lisa will have made a cake at six o’clock this evening.
→The action will be completed at six o’clock this evening.
4. (B) Lisa will have made a cake by six o’clock this evening.
→The action will be completed before six o’clock this evening.

5. (A) I will have worked in the company for 20 years next month.
→The action will have lasted (for) 20 years next month.
5. (A) I will have worked in the company for 20 years by next month.
→The action will have lasted (for) 20 years until next month.

 

[Charlie Bernstein]

Hello, dear teachers.
Could you please tell me if my understanding is correct? Thank you very much.

1. (A) Lisa will make a cake at three o’clock this afternoon.
→The action will start at three o’clock this afternoon.

Yes.

1. (B) Lisa will make a cake by three this afternoon.
→The action will start before three o’clock this afternoon.

Yes, and it will be completed no later than three.

2. Lisa will be making a cake at four o’clock this afternoon.
→The action will be in progress at four o’clock this afternoon.

Yes.

We can’t use “by” in place of “at” here.

We can use "by" to mean she will have started no later than four.

3. (A) Lisa will have been making a cake for two hours at five o’clock this afternoon.
→The action will have lasted (for) two hours at five o’clock this afternoon, and the action is temporary.

Yes.

3. (B) Lisa will have been making a cake for two hours by five o’clock this afternoon.
→The action will have lasted (for) two hours no later than five o’clock this afternoon, and the action is temporary.

See the correction.

4. (A) Lisa will have made a cake at six o’clock this evening.
→The action will be completed at six o’clock this evening.

It's grammatical and logical, but "by" would be more natural.

4. (B) Lisa will have made a cake by six o’clock this evening.
→The action will be completed before six o’clock this evening.

Yes.

5. (A) I will have worked in the company for twenty years next month.
→The action will have lasted (for) twenty years next month.

Yes.

5. (A) I will have worked in the company for twenty years by next month.
→The action will have lasted (for) twenty years [STRIKE]until[/STRIKE] next month.

This is grammatical but not natural. If you delete "by" it will be good.

You're getting good at this!