There are a number of sources for this type of information. The foremost reference book on the subject is probably the PDL HANDBOOK SERIES Effect of Creep and Other Time Related Factors on Plastics and Elastomers. You can obtain this book directly from the publisher using the following link:
You should be able to obtain this type of data from your resin vendor. I am not familiar with any standard 50% glass-filled nylons, so this may be a compounded grade from someone like LNP or RTP. Either way, you need to start by reviewing the data that they already have. If none exists, make them perform the necessary testing. Nylon producers like DuPont, Ticona, etc. have labs and personnel that are responsible for materials characterization so that customer's requirements such as yours' can be met.
then get the data from a PA supplier e.g ticona, and there you go!
Campus is a database merging program set up by the leading material suppliers. Each supplier measures their plastic materials to a standarised (ISO) method. They make this data available as a downloadable package, which is mergable in the Campus Program. Campusdata from the suppliers is usually available on their websites.
The Campus program merges and organises all data files from the different material suppliers, making searching easier.
The Campous data includes usually also creep diagrams.
Maybe some work to get the program and the data, but certainly worth while if you need data more often.
Good luck.