Trades are slightly more complicated (or complicateder) than turns are. You receive 10 every fifteen minutes per day, no matter what. But, on the top of each hour, you also receive an amount of trades equal to your Health/HP.
This means that if you're just starting off, a brand new player at 10 HP, you will receive 50 trades per hour. 10 at 15, 30, and 45 minutes past the hour and 20 at the hour. Remember to add the first 10 to your HP when calculating how many you'll be getting per day or hour.