Meaning of MOMENT in English
BAD : In that moment the door opened.
GOOD : At that moment the door opened.
in a moment = very soon: 'I'll have to go in a moment.'
at that moment = at that particular time: 'Just at that moment the telephone rang.'
BAD : At the moment the girl opened her eyes.
GOOD : At that moment the girl opened her eyes.
When you are telling a story or reporting what happened, use at that moment : 'At that moment the car skidded on the ice and went off the road.'
Compare: 'At the moment I'm working in a restaurant.' (= now, at the present time)
BAD : At the moment I saw him, I knew something was wrong.
GOOD : The moment I saw him, I knew something was wrong.
the moment (WITHOUT at ) = as soon as: 'He fell in love with Samantha the moment he set eyes on her.'
BAD : I'd like to see him in my office the moment he will arrive.
GOOD : I'd like to see him in my office the moment he arrives.
Longman Common Errors English vocabulary. Английский словарь распространенных ошибок Longman. 2012