I've been playing Ultima III like crazy, and I was just wondering if visiting the Time Lord is obligatory to beat Exodus or if he just provides clues. Can you go straight to Castle Exodus and just insert the cards in the right order or is the visit to the Time Lord required?

Thanks in advance!

No you don't have to speak to the time lord to defeat exodus so long as you know the order the cards go.

just in case you don't want to take my word for it (this is from Strategy wiki)
"The Time Lord can provide you with vital information about your quest. You'll find him on the eighth floor of the Time Awaits. Strictly speaking, you don't actually need to talk to him to complete the game."

[url=http://strategywiki.org/wiki/Ultima_III:_Exodus/Tips_and_Advice]http://strategywiki.org/wiki/Ultima_III:_Exodus/Tips_and_Advice[/url]

You don't need to visit him but I recommend it - his picture is hilarious :)