I think the word "good" (as in "good twenty minutes ago") is used to emphasize the "twenty minutes". The sentence is similar to "I booked a call to Brussels no less than twenty minutes ago and ...".

Norman's answer to your question is correct. Good is not often used in this way, but in the conversation you have given it is used to emphasise how much time has passed. So here are some other examples... I told you to come home a good hour ago and you are late!!!! I good deal of time has passed, but he hasn't finished the job. I have been waiting a good half hour. The dog took a good chunk of my food and ate it. (Chunk = piece) It is a little rude when used in these contexts because it is showing the person is frustrated or a bit surprised about the quantity in the sentence. Hope this helps!

Hi I, would say your name first so they know who you are if theys need to check their records. Then say 'could you assist me by speedingup.....End by saying'Thank you so much for your time, I really appreciate it, as this call is very important.'

agree with norman and malini.

I would change 'that' to 'this'. Other than that it looks good to me. A---Is that the Manager? =====> A---Is this the Manager?