I had been waiting ten minutes when the bus finally arrived. I was waiting ten minutes when the bus finally arrived. --first is better, because "waiting" is definitely complete when the bus arrives) I was walking home when I met Dave. Kate was watching television when we arrived. --these both imply a kind of interruption. Neither "walking home" nor "watching TV" were complete when Dave/we interrupted the action I am waiting FOR you. (Present Continuous) --no need to write a time, since the time is obviously "now" (you could write "now" if you wanted) I have been waiting FOR you for 10 minutes. (Present Perfect Continuous) --one of the main functions of PPC is to emphasise time. Out of context, this sentence expresses annoyance at the long time I've been waiting for you Yesterday at 10:30 I was waiting FOR you. --unlike "now", "the past" isn't a specific time Yesterday I had been waiting FOR you for ten minutes. ("for" necessarily?) --Same as PPC, this emphasises the time. "For" is necessary If we say How long - we use Perfect Continuous only? --Not at all :) How long did you wait for me? How long were you waiting for me? How long will you wait for her? Any tense is possible, there's nothing special about "how long" Kate was watching television when we arrived. (Past Continuous) Kate had been watching television for 2 hours when we arrived. (Past Perfect Continuous) --PPC states that she finished watching TV shortly before we arrived. The first just implies we interrupted her. They had been waiting for ten minutes when the bus finally arrived. They were speaking when the bus finally arrived. --Same thing. #1 emphasises duration, #2 says their conversation wasn't finished They are speaking and waiting for the bus. They have been speaking and waiting for the bus since 7 pm. Hope this helped!

The difference is the "ten minutes" more than anything to do with the time sequence analogy in your other examples. The continuous describes what you were doing in that time. To see this, try introducing the phrase into your other examples. E.g. "I had been walking for ten minutes when I met Dave".

Thanks Gürsel!

Hi, I would say; I had been waiting for 10 minutes when the bus finally arrived. Because first act. is before second act. which is already in the past