"How long (hours of play) should i spend on each world"?
Hmm. You know, I have no idea. It's kind of random. That's a hard question, that I really don't know a solid answer to.
BUT, if I was to come to a guess and make a recommendation, it would be this: 2 hours a day to beat the game in 2 months with no sidequests, spending 2.5 hours per area.
Here's how I came to that guess: It all hinges on the amount of time you get to play Wizard101 during the day. If you have multiple hours to play during the day, then you should be just fine taking on all the side quests in all the worlds. If you don't, then perhaps you'll only want to take on the story line quests in the world.
There are approximately 50 (or so) main storyline quests in each main world leading up to Malistaire (That's a rough guess with round numbers). Let's give you 30 minutes to complete each quest (some take less, some take more). That means that each world in the spiral should take you 1500 minutes (so around 25 hours) to complete the main story arc. Let's say each world averages 10 quest zones, that puts you at 2.5 hours per area, just doing main story quests.
With those maths it puts you at 125 hours of play time. Dividing that by 60 days means (sans interruptions, sans playing with your pets, sans hanging out, sans decorating your house, sans Grizzleheim, sans side quests including zeke quests) you should play a little more than 2 hours a day to beat the game in 2 months.
Now, the moment I hit the publish button you will start to see comments come in that either refute what I'm saying or agree with it. Probably mostly refute it. It's a really hard question and it's really subjective . . . it doesn't account for group set up, deck set up, interruptions, etc. (it doesn't account for a lot of things)
BUT I SHALL NOT FEAR THE PUBLISH BUTTON! You asked a question, I gave an answer. /shrug
You should read the comments. Someone in there might have a better guess than me.
Best of luck,