I was told that if you purchase tickets later in the day they are cheaper since they are like half day tickets. Is this true and if so does anyone know how much they are?

No half-price tickets that I am aware of.

I was told that if you purchase tickets later in the day they are cheaper since they are like half day tickets. Is this true and if so does anyone know how much they are?
They haven't done this since the 70s. BUT, if you are with a convention, they often do have tickets called "Twilight" tickets, and are usually about $45-50 and good after 4pm.

You might be thinking of Knott's Berry Farm, which offers 1/2 price adult tickets after 4 p.m. when the park is open later than 6. They also used to charge the reduced children's price for expectant mothers (since you can't ride all the wild rides), but I see no mention of that discount on the website.:)