"PM meeting" is short for "afternoon meeting" and refers to a gathering or appointment that takes place in the afternoon, typically after 12:00 pm or midday. Full definition
Low Season (May - Oct) 9:30 am, 12:30 pm meeting at Punta de Mita Location. (wildmex.com)
He made his shock announcement to a 5.15 pm meeting of Liberal Democrat MPs at Westminster, saying he had now done all the things he had set out to do for the party. (theguardian.com)