Note: This was written as an extra scene for the book and doesn't work as well when taken as part of the movie. I highly recommend the book if you haven't read it; it's very entertaining and does not detract from the film experience at all.
The time was 5:38. It was annoying, telling your limbs to move and getting such a slow, sluggish response when they did. However, Westley kept walking, knowing he had to keep his strength up if he were to be strong enough to face Humperdinck. (To be quite honest, Westley didn't think for a moment that he would have to face the Prince. Inigo was going to handle things with the Count, he was sure of it, and the groom of the night, if he was unfortunate enough to come across Westley, would probably get pounded on by Fezzik. However, just in case, he kept moving.)
As he waited for the giant to return from helping Inigo, however, he heard a sound. Voices from an adjoining corridor. Probably soldiers come to rid the castle of their intruders. Without thinking, Westley slowly hobbled through the nearest doorway into the next corridor, closing the door behind him as quietly as possible so as not to alert anyone. (In truth, those voices he heard was no one of importance, just some citizens coming for the wedding who had managed to get near enough to be heard, but of course he couldn't tell the difference in his current state.)
A loud roar was heard. For an instant, Westley believed it was a member of the Brute Squad that had probably spotted Fezzik and Inigo, but then, remembering how they had scared off the entire Brute Squad breaking into the castle, he realized it must have been Fezzik he had heard. The soldiers Westley had heard must have caught up to the giant. He wasn't worried, as he was sure Fezzik could take care of the bunch, especially if what he'd said was true all that time ago about him being used to fighting against groups.
Westley paused for a moment only a foot from the door he had just come from, gathering what little strength he had. As he did, he thought about Buttercup, and picturing her gave him a motivation to keep going. He forcefully lifted up his foot and began moving forward again, trying to decide where exactly she would be at this moment.
The Count had attacked them mere moments after they had entered the castle, leading Westley to the conclusion (though it was hard to admit to himself) that the wedding was over, and the only reason he knew it had begun was because he had heard the Archdean's voice. (Anyone and everyone who had lived in Florin a reasonable amount of time would know what that voice sounded like. Ever since then, even up to today, the Archdeans tended to have a rather odd accent, be it planned or by sheer luck. Either way, the Florinese are always entertained.) Since Buttercup was now Humperdinck's bride (he felt a little stab in his heart at just the thought of it), the only reasonable place Westley could of that she would be was the Prince's bedchamber.
He reached the next door and threw his head over to look inside. It seemed to be a dining or a meeting room of some sort, with a table at the center, chairs all around it, and nothing else. The room was practically empty.
Moving along, he began thinking of just where Humperdinck's chamber would be. His first thought was that it would be upstairs somewhere, which sent his heart plummeting as he knew he wouldn't be able to climb the stairs in his current condition. However, the more he thought about it, the more he was convinced this was incorrect. The Prince's true love was hunting, so he would prefer to be on the ground floor, probably as near the Zoo of Death as he could be.
That was when Westley made yet one more realization: the hallway he was in coincidentally (this was before coincidences, though just barely; the word would first be used retelling this very story) was right next to the Zoo of Death.
Confident he was headed in the right direction, Westley pushed ahead as fast as he could, which, granted, was not very fast, but it was significantly faster than he had been moving beforehand. He looked into each and every room he passed until he found the bedchamber. Though he didn't see Buttercup, he took a step inside to look around.
There was no doubt in his mind that this room belonged to Humperdinck, what with the weapons against the wall that he undoubtedly used for hunting and the way the room was lavishly decorated. However, Westley wasn't here to bask in the decorations, so he continued looking for his love without saying a word so as not to alert anyone who happened to be nearby. As he continued walking around, he could feel himself begin to slow down against his own volition, weakness returning to his body. This was troubling as he was becoming more and more certain that she was not in this room. By the time he reached the bed, he felt his legs wobbling and realized that he was going to collapse at any minute. He still had about a half hour until Miracle Max's pill wore off (in reality only ten minutes, but he didn't know that), so he believed the weakness returning to his legs was due to the small boost of speed he had given himself back in the hall.
Sighing, he climbed onto the bed, not really sure what else he could do. At the very least, the Prince would probably stop by at some point or another, maybe even accompanied by Buttercup. Until then, though, all he could do was wait. The time was 5:45.