Time/Date Capture when data is entered and multi conditional

Not sure if you really need code. If you want the calculations to only occur "each time the spreadsheet is opened," then you should put the code in the workbook as a Workbook_Open event.

However, why not just use formulas?
1. =if(isnumber(C1),now()-c1,"")
2. =if(and(isnumber(c1), isnumber(h1)),h1-c1,"")
Note: if you only want to display hours, then you would use a custom number format of [h] or [h].mm
3. =if(isnumber(L1), L1*F1,"")
Custom format as [h].mm.ss

Okay, I think you want to use a Table. You can create one by highlighting a cell in your table and then hitting Ctrl-T. This creates a Table object (aka List pre-2007, I think) that has the nice feature of copying down equations when you add a new row. This means you don't have a lot of unused rows with 'empty' forumlae in them. Play around with it a bit, and you will see what I mean - go to the row just below your Table and add some info - the Table will automatically expand down and will populate the new row with any equations that were in the row above it.
This will allow you to find the first empty row after your data. Then you can add the data to the bottom row, and when it is added, the table will expand down to include your data, and will copy down any formulas. I think that will work for you. The only caveat is that I remember from VBA, just adding the data below the table will not cause the table to auto-expand. I know I solved a problem like that in the past, but I can't quite find it. I think this thread may have a key part of it, though, by using the .Add method to a table. I think that does it. If not, let me know and I can dig deeper (although I think I used 'Record Macro' to see how to do it in VBA).
Alternatively, your user form can decide which column to look at for the last 'real' line in your data. Is there a column which is populated when there is data, but empty (i.e. no formula) when there is no data? Search that column to find your true new line.