I had an issue with the datetime picker at 4.18 and created a support ticket with Esri. That has been turned into enhancement #ENH-000138560, which is still open. I think this is the same issue that you are having, and if the enhancement is still open (it is) that means it wasn't fixed at 4.19.
My application has related tables that I'm using Dojo Dgrid for, which has a datetime picker, but I also utilize the ArcGIS Editor for the primary feature layer, which has the datetime picker problem. In my case, I'm moving forward with what I have with the expectation of updating it once this is fixed. I have spent a little time trying to build one on top of the Editor widget, but I never figured a way to make a custom datetime picker for it. If you figure something out please let me know.