Well if you buy the farsight alteration, it gives you a fragile visible permanent ward (I know, hardly an excuse for an actual ward) but you can ward every minute with it and it doesn't count towards ward limit so you could in theory place around 20 of those wards (from the point you reach lvl 9)
Normal trinket wards' recharge time and duration gradually improve throughout the game but it's about 2 minutes 20 seconds when all mashed together (don't know the correct math on that one) which means you can put about one ward every 2:10 or 2:20 from minute one. That would count into around 15-20 wards max in a 40 minute game.