need a count system for header

[TheSupportForum]

Hi Programmers

i need the following system of date shown in my header

1) customer days
Day 1
Day 2
and so on....
it will then update at 08:00 GMT
Day 3.... and so on

so heres what i need in more details

each day is a new day but the day starts from 08:00 GMT and ends at 08:00 GMT the following day, each day will count up from a date and show as

Day 1,755 instead of a full date