Transactional CSAT Survey Distribution Timing

We currently have an intentional delay of six hours built into our transactional CSAT survey distribution. We're looking to shorten that, but would like to do it in an informed way, so are looking for best practice. Gartner suggests that 84% send surveys "immediately", but offer no further definition of what that means (their next category is >1day). If you can let me know what your approach is, and offer the rationale for your current approach, that would be really helpful. Thanks!