I've had an aborted take off at LCY - no explanation just "we'll have another go" which was not particularly encouraging.

I had a go-around at SFO on UA. I was listening to ATC (available on Ch9 of UA's audio) and clearly heard the preceding plane being given the hurry up so it was no surprise for me when the go around instruction came. Difficult to say how low we were as it's over water at SFO but I would guess a maximum of 20 seconds before landing.