HRV takes several weeks of data before it’s useful. One or two random readings are pretty much worthless.
After you have several weeks of good data, fluctuations in over night HRV (I believe the preferred method is an average of the entire nights sleep) have been shown to correlate pretty accurately with someone’s body struggling to recover. It could be from work stress, training stress or drinking too much alcohol. Either way over night HRV can be useful.