The guidelines on starting the Pill are stated as such due to the risk of becoming pregnant during the first week of the Pill as your body adjusts to the hormones...for example...for Ortho Tri Cyclen...
Sunday Start: starting on a Sunday means you have to use a 2nd method of contraception (ie. condom) for 1 week to make sure you don't get pregnant as your body adjusts to the pill.
Starting on the 1st day of your menstral cycle: the Pill is immediately effective against contraception (because it is highly unlikely that one will become pregnant while menstration is occuring anyways!)
If you are not sexually active, and you are using the pill for acne or other hormonal reasons, you can start the pill on ANY day of the week. It is true that your cycle can be a little messed up at first and you may have some spotting during your first month on the pill. The Pill is not a miracle and it can take months to clear up acne, so be patient and keep taking it. =) This information is from me, a pharmacy student here in the US, and as always, you should follow the guidance of your medical supervisors. =p