If you use Heroku and New Relic, make sure you install the gem we wrote to make New Relic report correct queue times: https://github.com/RapGenius/heroku-true-relic
I don't recommend that you use this patch - work needs to be done on Heroku's end, this is not a satisfactory workaround. The ideal would be for them to add a timestamp to the headers at the front end of the dyno machine (i.e. in apache/nginx/whatever) to allow the calculation to include a local-machine-relative timestamp rather than one reliant on two servers being in sync.
The major issue is that servers on AWS do not have synchronized clocks, in general. I'm not sure how Heroku manage their servers, but I do know that in the samples I saw several years ago, we had a very large variance in the queue time reported based solely on that clock skew.
The New Relic reported value is an average, which is a poor choice for something like this, but it's very difficult to graphically illustrate queue time across a network of machines without resorting to it.
I'd be happy to discuss it further, and I know that sgrock [1] is also around the neighborhood - he's one of the current Ruby Agent maintainers.