Co." on the movement, and with an "American Standard" only case signature, pre-dates April 1923.Narrowing down the date beyond that with certainty may not be possible based on current information.
Though we have far more of these early watches than we did a year ago, we still have relatively few upon which to base conclusions.
No doubt, some aspects of these conclusions will change over time as more examples are collected.
For example, movements made prior to 1924 do not bear the standard movement date code found on watches dated 1924 through 1949.
(For a list of those codes, visit Bulova Date Codes.) Additionally, the case serial numbers on those early watches tend to begin with "1" or "2" and appear to bear no correlation to the date the watch was made.
Consultation with online movement lists may provide at least ballpark information regarding the date of the watch. However, it is important to note that all such movement lists are based on observations of examples rather than any official Bulova documentation.