1 - Not sure if there's a quick way to do it
2 - While in the calendar hit Control-G (for Go To) and enter the date and a
addition or subtraction and it'll work. For example:
10/21/2005 + 90d should go 90 days out from today

1) No. While Outlook easily moves to a specific number of days after a date,
it can't easily calculate how many days between day 1 and day 2. Excel has a
formula that does it easily and I believe that chameleon clock and 1st clock
can do it too.

2) Moving ahead is easy - if you are moving ahead from the date in an open
appointment form, type 4d and outlook enters the date 4 days from the day
originally in the form. Or use Go to (Ctrl+g) to move there. Backwards is a
harder - you need to type 'before - outlook doesn't accept - (minus sign).

http://www.slipstick.com/emo/2005/up050818.htm#naturaldate
http://www.outlook-tips.net/archives/2003/20030721.htm