So, there are still questions about your layout/data that affect the options that might be available.
The problem you have with what you say you want to do is that Excel cannot take data that is in a cell and use it in a formula that over-writes that data in the same cell. When you put the new formula in, the previous data is gone and no longer available. The formula must use data that exists at the same time in another cell.
Here is a possible scenario if this matches the layout of your data. If not, then there might be some other alternatives, but we would need to know the layout in order to go any further in helping you. This layout seems like it may match with your layout.

If your data is in groups of two as in Column C above, you could enter formulas in any column as in Column E above (formulas written out in Column F) to put the data in a separate column and hide the original column. Or, if you need the layout to follow a particular look, these formulas could be put on a separate sheet in Column C giving you the same appearance as if the two pieces of data had been combined in C2, C4, C6, etc.
In order to drag these formulas in the groups of two, select both formulas as in E1:E2 above and drag the fill handle down which will alternate the two formulas all the way down.
If your data doesn't stay with the alternating label/time example, we would need to have more information about how it is laid out to proceed.
Reply if you have additional questions or information. Please mark this reply as answered if this solves your question.
Rich~M