Here is an Excel formula that does what I think you want:
=IF(LEFT(A1,6)=TEXT(NOW(),"yymmdd"),TEXT(NOW(),"yymmdd")&"CZ"&MID(A1,9,LEN(A1)-8)+1,TEXT(NOW(),"yymmdd")&"CZ1")
This assumes that you have a value in A1, and this formula is being entered into cell A2. Adjust accordingly.
Basically, what this does is look at the value in the cell above it. If today is the same date as the cell above, it will add one to the counter at the end of the counter. Otherwise, it will start over at 1 again. So the result would look something like this:
A1: 050119CZ1
A2: 050120CZ1
A3: 050120CZ2
...