Thanks enzso for this post https://www.ozbargain.com.au/node/390272 i have now used this hack a few times!
I did another booking again just then and got a nice surprise! They are doing a special at the moment where one half hour parking at T123 is now $5 or you can add 2 coffees for $10 all up.
Not sure when this special offer is going to end but hope this helps someone! Ends 30 September 2018.
Also, thanks jiakz for pointing it out, it's 1 hour for $5 + 1 hour grace period before + 1 hour grace period after.
Update: Just found out more about this offer https://www.melbourneairport.com.au/Passengers/Parking/Speci…
"The Offers - 1 hour terminal parking for $5 (Parking Offer) and/or 1 hour terminal parking plus 2 Hudsons coffees for $10 (Coffee Offer). The Offers are valid for online bookings only made at www.melbourneairport.com.au/parking, cannot be cancelled and are non-refundable.
Bookings must be made before 11:59PM on 30 September 2018 for car park exits before 11:59PM on 30 September 2018 and are subject to the Melbourne Airport Parking Online Booking Terms and Conditions.
The Parking Offer includes 1 hour parking at the ‘At Terminal’ T123 car park. The Coffee Offer includes 1 hour parking at the ‘At Terminal’ T123 car park plus two standard coffees redeemable at any Hudsons Coffee outlets at Melbourne Airport (subject to Hudsons store trading hours) on the same day as the day of parking and upon presentation of a valid booking confirmation which includes the coffee voucher. The Coffee Offer can only be redeemed once.
Melbourne Airport reserves the right to withdraw The Offers from sale at any time without notice (subject to honouring any Offers already purchased prior to the date of withdrawal). The Offers cannot be used in conjunction with any other offers and are not valid for Melbourne Airport employees or valid ASIC cardholders."
Any other carparks that offer the 1hr grace period on either side?
This would be great if all parking that allows online bookings had this loophole.