Sum in Matrix with condition

Hi! I have the following issue: I have a big matrix, for example 1000x12. The values in one row are 5-min-precipitation-measurements (12*5 min= 1 hour).I have to build a sum of the measurement values>0, under the condition that there are at least 3 hours difference between the end of one and the beginning of the next precipitation event. If the difference between sums is less than 3 hours, the sums should be put together in one. The Date and Hour are saved in a separate vector.

Example for Precipitation matrix:

1  0  1  0  26  32  41  41  47  50  44  36
0  0  0  0  0  1  0  0  0  0  10  10
0  0  1  4  7  8  7  7  4  1  0  0
0  0  7  5  2  1  0  0  0  0  13  14
5  6  5  4  0  0  0  0  2  1  2  0
0  0  0  0  0  0  0  0  0  0  4  1
0  0  0  0  0  0  1  0  2  3  5  3
0  0  0  0  0  0  0  2  0  0  0  0
0  0  6  5  2  5  1  2  0  0  6  6
0  0  0  0  0  0  2  1  0  0  0  0
0  0  0  0  0  0  35  39  49  50  49  129
50  194  708  832  150  103  49  49  40  25  17  36
49  50  214  328  311  215  104  104  153  139  127  105
49  50  49  50  49  50  49  40  35  29  18  24
23  13  1  1  4  16  46  50  49  50  49  50 
.
.
.

Example for Date Vector:

'20-Jan-1965 14:00:00'
'20-Jan-1965 16:00:00'
'20-Jan-1965 17:00:00'
'20-Jan-1965 18:00:00'
'20-Jan-1965 20:00:00'
'20-Jan-1965 21:00:00'
'20-Jan-1965 23:00:00'
'21-Jan-1965 00:00:00'
'21-Jan-1965 01:00:00'
'21-Jan-1965 02:00:00'
'21-Jan-1965 04:00:00'
'21-Jan-1965 05:00:00'
'21-Jan-1965 06:00:00'
'21-Jan-1965 07:00:00'
'21-Jan-1965 08:00:00'
. 
.
.

Can someone help? Thanks!!