I had at first misinterpreted the timestamp implementation of OAuth into thinking that it meant a timestamp that was not within 30 seconds past the current time would be denied, it turned out this was wrong for a few reasons including the fact that we could not guarantee that each system clock was in sync enough down to the minutes and seconds regardless of time zone. Then I read it again to get more clarity:
"Unless otherwise specified by the Service Provider, the timestamp is expressed in the number of seconds since January 1, 1970 00:00:00 GMT. The timestamp value MUST be a positive integer and MUST be equal or greater than the timestamp used in previous requests."
source: http://oauth.net/core/1.0/#nonce
Meaning the timestamps are only compared in relation to previous requests from the same source, not in comparison to my server system clock.
Then I read a more detailed description here: http://hueniverse.com/2008/10/beginners-guide-to-oauth-part-iii-security-architecture/
(TL;DR? - skip to the bold parts below)
To prevent compromised requests from being used again (replayed), OAuth uses a nonce and timestamp. The term nonce means ‘number used once’ and is a unique and usually random string that is meant to uniquely identify each signed request. By having a unique identifier for each request, the Service Provider is able to prevent requests from being used more than once. This means the Consumer generates a unique string for each request sent to the Service Provider, and the Service Provider keeps track of all the nonces used to prevent them from being used a second time. Since the nonce value is included in the sign