Is this something you expect to do repeatably i.e similar to a scuba bottle filling operation, or it more of a infrequent transfer requirement; and, how accurate and repeatable does the calculated time need to be?
Also, what are the delivery and receiving pressures for your transfer(s), for pressures above 1000 psig there is also a pressure factor Z (pressure vs mass is not linear at high pressures) that has to be incorporated into the calculation.
Part of the problem is that a tighter accuracy for the time for an amount (lbs) of gas delivered at the filled tank pressure requires an increasing amounts of data input and operating restrictions for the operator(s) if the calculation is to be of assistance; and, for frequent sequential fillings this can become a major issue.
A few years back, on another forum, there was an inquiry asking if someone could develop an "accurate" program for calculating the number of bottles of a given size and pressure limit that could be filled from a given air storage tank supply. While Bauer Storage Systems has data on this issue, they state that their data is based upon an ambient constant temperature (i.e. Isothermal) transfer.
At the time, I didn't see developing such a program as being a particularly difficult problem; however, after about four months of intensive work, multiple program revisions using verifying fill testing by the requester, it was becoming clear that due the many associated factors in this process that such a program might not be attainable; and a month or so later it became clear that accurately predicting the filling was not going be achieved, at least by my efforts. The final issue that killed the project was accurately calculating the heat loss rate from the receiving bottle as its gas temperature rises during the filling and the heat gain of the supply tank as its temperature falls during filling and rises between fillings.