Had a nice flight today, an Estes Mammoth on a F15-6. On board we had a Jolly Logic Altimeter3 and a Chute Release set for 300ft. All went as expected as you can see on the chart provided by the Alt3, CR opened chute right on time.
Did you use a drogue? If not, then please consider heading over to this other thread and post your data there, should be useful. Looks to me about 40 ft/sec descent rate before the main chute opened up, based on the graph, but maybe the Alt3 reported the number separately as well.