adding a formula upto the last row of data

Every day i have to pull of a text document from a server and import it into excel so i can change the format of certain columns. Then import the data into a database. I am trying to create a macro that will enable me to make these changes instantly without having to spend minutes on them.

There is once column that has the format 2009-03-12-10:02:09 which indicates date and time however there is a - inbetween them. I know that i can use =DateValue(left(a1,10))+ Time alue(right(a1,8)) and then format the cells to date and time to remove the -. My issue is that i only want to use the formula upto the last row of data otherwise i end up importing blank rows into my database.

Does anyone know of a way i can do this?