I have file with this type of format

01.02.09 08:30
bob
jill
mark

01.04.09 07:00
bob
jill
mark
tom

I want to count the names after the date /ime line (01.02.09 08:30) and add that number after the time like this

01.02.09 08:30 3
01.04.09 07:00 4

I don't care about the names after the count so I can leave them or strip the out with sed if it simplifies the process. I could also redirect the output of date/time and count to second file if it makes it simpler. The only thing I really need is the date/time and number on the same line.

What is the best tool to accomplish this and can someone provide an example?