Why is UTC activation time referred to 30W in NAT-OTS? I am reading the NORTH ATLANTIC OPERATIONS AND AIRSPACE MANUAL and I came across the following statement more than once during my reading:


  The activation time of the westbound OTS shall be published as 1130z
  to 1900z at 30W.
  
  The activation time of the eastbound OTS shall be published as 0100z to
  0800z at 30W.


You can find this quotes at page 175 of the link provided above.

Here is my question: if the activation times are expressed as ZULU time (therefore as UTC), why is it specified at 30W? As far as I know a ZULU time is referred to the Greenwich meridian and therefore at 0W. To me it sounds quite contradictory to express an UTC time by specifying a longitude different than 0. 

What am I misinterpreting? What is the right interpretation of the quotes presented above?
Think of 30W as a kind of traffic marker for flight planning.
If your planned route is going to cross 30W before the tracks activate (that is, ahead of the traffic flow), then you can file "random route." If you're crossing 30W during the active period, then you have to file on one of the tracks unless you can climb above them before crossing the entry fix.
This also works going against the flow: if you're crossing 30W in the opposite direction during the active period, you'll have to route either north or south of the tracks unless you can get above the NAT FL's before your entry fix.
As far as Zulu goes, it's just the common reference everyone uses (therefore, "Universal Coordinated Time").