Calculating cycle time based on different criteria

I am trying to use DAYS to calculate cycle time based on Job Type, which would be simple enough, but I'd like to use the IF(L2="","",....) to leave the cell blank if the cycle is not complete. If the Job Type is "Spec", then I need the formula in M2 to calculate the days calculated between L2 and I2, if "Build", then I need days between L2 and F2.

Again, this wouldn't normally be a problem for me, but as I said I'm trying to get the cell M2 to be blank if L2 is also blank (cycle not yet complete). Is this just not possible without a separate reference cell or something? Can someone help? I've been trying to use IFS and nested IF statements, but I think that perhaps I'm getting my order of logic messed up. 

(sample file attached for reference)