Sorry for the confusing title.
Here is what I would like to do:-
1. I have a multiple column table, one of which has time stamp and another
one has an entry in multiple lines, because of better visibility. Therefore
the table looks something like this:-

|--------+--------|
| DATE 1 | line 1 |
|        | line 2 |
|        | line 3 |
|--------+--------|
| Date 2 | line 1 |
|        | line 2 |
|        | line 3 |
|        | line 4 |
|--------+--------|

2. I would like to sort the table based on date, but instead of sorting
each line is it possible to sort by block (defined by the horizontal
lines.)?

I must say I did not find time to do an extensive search to find a
solution- therefore a pointer to another post or some URL will be very
welcome.

Thanks
Deb