- The fact that your data look like an exponential and the the inter-event time in a Poisson process is exponential doesn't carry any logical implication that there's a Poisson process operating here. [It would be an argument analogous to "snow is cold and frozen chicken is cold, therefore frozen chicken is snow".]
Certainly if you're certain that a Poisson process holds (or is so close to holding it will make little difference to the way the process behaves), you'd expect an exponential inter-event time (or nearly so). But there's nothing inherent in "time to process a work order" that makes it specifically exponential. It does happen that many such sets of time-data are reasonably well modelled by an exponential, but on the other hand, many are not. [e.g. It's not hard to think of reasons why some things would not be exponential -- consider if inherent in every work order was two days worth of paperwork, even for a one day job); then the distribution could not be exponential, but might be close enough to a shifted-exponential. Or imagine if every job had two consecutive parts, both of which were close to exponential in their completion time; then the overall completion time would not be exponential.]
It sounds like your recorded data may not be close to continuous. You've got a discrete number of days, and exponential isn't discrete. (The underlying time may be continuous but from my understanding you only have days recorded. You might consider whether you are better off using the geometric - the discrete "equivalent" - to deal with the data at hand.)
Even the underlying time won't be exponential; however, it might well be close enough for your purposes (which is to say, even though I could fairly safely deny that your distribution is exactly either exponential or geometric, I would probably just go ahead and use it too, since it will probably serve quite well).
However, I want to raise some potential censoring issues
a. You mention $x<1000$. Is this a hard recording limit (i.e. censoring), or is it that you just haven't seen a job that takes so long (in which case it's of a different kind than the "$0<x$" part? After all, a job that takes "-3 days" isn't simply a value "not yet seen" but more "not ever possible for real completion times")
b. Incidentally, can you have a work order that is "just given up on" because no solution is available, where you're recording the time until the problem is shelved?