|this is a bit tricky!|
Got it to work using the DMIN function.
Note this formula requires you to have headings at the top, and you'll need to hide some columns and rows that I'll be using. I'm assuming that your list starts in cell B1, and is 100 lines long including header rows.
So in cell A1 (insert a column and row if needs be) type in "Status"
In cell A2 (insert another row) type in "WAITING"
In cell B2 (insert another column) type in
this will give you the lowest time that exists that matches the criteria (namely, that are still waiting).
So leave in your existing conditional formatting but you need to have a new first condition:
cell formula | equal to | =AND(J4="WAITING",E4=$B$2)
Note this is the conditional formatting on cell J4 (status, first row)...obviously you'll need to amend the row number and possibly the columns depending on how your data is set out.
You can hide columns A and B, and rows 1 and 2 or just put them outside your print area.
Apologies it's a bit long-winded, hopefully someone can come up with a better solution!