What is your need for 48 hour rainfall as it's not a standard time frame for rainfall?
sum48h will not work as it is not supported and is possibly behind the time frame point of high resolution data availability to compute the value? sum30h I know will work with rainfall as this is specific to some countries that report say from 9am to 9am and do an interim report for the 6 hours to 3pm, using sum30h and sum6h allows for the 6 hour rainfall to 3pm and the difference provides the 24 hour rainfall to 9am or essentially available for any previous 30 hour period from any point in time.
I need the value for 48 hours because the monitoring systems active in Sardinia use this time interval ( example http://www.sardegnacedoc.it/idrografico/temporeale ). I need to put the data of the Sardinia monitoring system together with my data.