Most rides at Thorpe were done on a guesstimation. Rush's queue at least was broken up into 6 segments (Main start, Main end, Extension 1 out, Extension 1 return, Extension 2 out, Extension 2 return) but a couple operators tended to consider it as 3, and that's how it was described in the rulebook - Main, Ext. 1 and Ext. 2. Main was a 10 minute queue, Ext. 1 was an additional 15, Ext. 2 was an additional 20.
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Take this queue sketch as an example. Merlin queues are split into distinct sections which
could be subdivided into an outbound and a return (illustrated as dark and light), but Merlin only note what I've illustrated as red, gold and blue as 3 sections. I've seen Rush advertised as 45 mins when it's only been halfway along the 2nd extension, which should only be a 22.5 min wait.