At present, Season 14 is expected to begin one week after the end of Season 13. If this follows the pattern of previous seasons this expansion, we're on track for patch 5.4 to drop the same day as Season 13's end (Patch 5.2 dropped on March 5th, the same day Season 12 ended) or within that one week period. So this is a really good benchmark for how close we are to patch 5.4 - it won't come before the end of Season 13, but it may come that day.
Keeping in mind that there can always be delays, dates can be moved back, and that no date for patch 5.4 has been announced, it definitely feels like it's getting closer. For the full announcement leap behind the cut with us.