This tells you how long every mission takes on average without skipping the videos.

Mission 1 - The Party - Takes around 6 minutes to complete.
Mission 2 - Back Alley Brawl - Takes around 6 minutes to complete.
Mission 3 - Jury Fury - Takes around 5 minutes to complete.
Mission 4 - Riot - Takes around 4 minutes to complete.
Mission 5 - Road Kill - Takes around 3 minutes to complete.
Mission 6 - Four Iron - Takes around 6 minutes to complete.
Mission 7 - Demolition Man - Takes around 8 minutes to complete.
Mission 8 - Treacherous Swine - Takes around 4 minutes to complete.
Mission 9 - Mall Shootout - Takes around 5 minutes to complete.
Mission 10 - Waste The Wife - Takes around 3 minutes to complete.
Mission 11 - Guardian Angels - Takes around 7 minutes to complete.
Mission 12 - The Chase - Takes around 6 minutes to complete.
Mission 13 - Phnom Penh '86 - Takes around 7 minutes to complete.
Mission 14 - Two Bit Hit - Takes around 5 minutes to complete.
Mission 15 - Sir, Yes Sir - Takes around 4 minutes to complete.
Mission 16 - The Fastest Boat - Takes around 5 minutes to complete.
Mission 17 - Autocide - Takes around 8 minutes to complete.
Mission 18 - Supply & Demand - Takes around 5 minutes to complete.
Mission 19 - Stunt Boat Challenge - Takes around 5 minutes to complete.
Mission 20 - Cannon Fodder - Takes around 6 minutes to complete.
Mission 21 - Naval Engagement - Takes around 6 minutes to complete.
Mission 22 - Juju Scramble - Takes around 5 minutes to complete.
Mission 23 - Bombs Away - Takes around 5 minutes to complete.
Mission 24 - Dirty Lickin's - Takes about 4 minutes to complete.
Mission 25 - Trojan Voodoo - Takes around 6 minutes to complete.
Mission 26 - Death Row - Takes around 6 minutes to complete.
Mission 27 - All Hands On Deck - Takes around 8 minutes to complete.
Mission 28 - Rub Out - Takes around 7 minutes to complete.
Mission 29 - Shakedown - Takes around 7 minutes to complete.
Mission 30 - Check Out At The Check In - Takes around 6 minutes to complete.
Mission 31 - Bar Brawl - Takes around 4 minutes to complete.
Mission 32 - Cop Land - Takes around 8-9 minutes to complete.
Mission 33 - Love Juice - Takes around 6 minutes to complete.
Mission 34 - Psycho Killer - Takes around 2 minutes to complete.
Mission 35 - Alloy Wheels Of Steel - Takes around 3-4 minutes to complete.
Mission 36 - Messing With The Man - Takes around 2 minutes to complete.
Mission 37 - Hog Tied - Takes around 4 minutes to complete.
Mission 38 - Publicity Tour - Takes around 5 minutes to complete.
Mission 39 - No Escape - Takes around 5 minutes to complete.
Mission 40 - The Shootist - Takes around 9 minutes to complete.
Mission 41 - Loose Ends - Takes around 4 minutes to complete.
Mission 42 - The Driver - Takes around 4 minutes to complete.
Mission 43 - The Job - Takes around 8 minutes to complete.
Mission 44 - Gun Runner - Takes around 8-9 minutes to complete.
Mission 45 - Boomshine Saigon - Takes around 3 minutes to complete.
Mission 46 - VIP - Takes around 3 minutes to complete.
Mission 47 - Friendly Rivalry - Takes around 3 minuted to complete.
Mission 48 - Cabmaggendon - Takes around 5 minutes to complete.
Mission 49 - Checkpoint Charlie - Takes around 3 minutes to complete.
Mission 50 - Distribution - Takes around 5-10 minutes to complete.
Mission 51 - Spilling The Beans - Takes around 7-8 minutes to complete. 
Mission 52 - Hit The Courier - Takes around 4 minutes to complete.
Mission 53 - Cap The Collector - Takes around 6-7 minutes to complete.
Mission 54 - Recruitment Drive - Takes around 8 minutes to complete.
Mission 55 - Dildo Dodo - Takes around 4-5 minutes to complete.
Mission 56 - Martha's Mug Shot - Takes around 8 minutes to complete.
Mission 57 - G-Spotlight - Takes around 7 minutes to complete.
Mission 58 - Keep Your Friends Close - Takes around 9 minutes to complete.

I hope this helps and you could learn facts and see info about the longest, shortest & how long missions take! Thanks a lot, I will give you info about anything else just contact me on my Youtube channel 96lw15 !!! Bye;)x