Pirwin, I sympathize. I have the same issue. It occurs to me that you could create a form, in which each number pair would be typed in a field, with colons in between the fields. In a form, properly set up, after typing in a field, a tab sends you to the next.
Also, though I'm not sure if Word fields can do this, you are surely familiar with web forms that automatically advance your cursor to the next field once the requisite number has been entered in the previous. The only issue in this case, would be whether you need to type other text, e.g., actors' lines, after one time code, prior to entering the next TC.
Once the field:field:field:field is created in one cell, it can be quickly copied to the others in the column. You can look up forms; you have to protect the form before you can type in the fields.