Both answers are correct... well sort of! The 60 seconds applies to ATC and the 30 secs in the AIP reference to pilots...
So if the pilot gets a time they must meet it +/- 30 seconds; however if the ATC gives you speed and vectors etc; instead of time, the ATC tollerance is 60 seconds...
There may be circumstances when the ATC gives you a time, which has already been adjusted for the ATC tolerance. So the ATC is expecting you to be within 30 seconds as they have already used their tollerance....
E.G. MAESTRO says ARBEY 30 then 250KTS, but due to traffic considerations the ATC gives you 31, if you turn up at 32 there will be a gap, if you get there at 31.5 we can probably make it up with an abreviated circuit or adjusted speed. and if you get there at 30.5 nobody will notice... well sort of, but you get what I mean.
sorry no reference included, but will try and find later.