When should the dealer muck folded hands at showdown?

[redfisher]

2/5 NL game. I'm holding AK and raise to 20. 2 callers behind me + the BB. Board is all rags, no flush but some odd straights are possible. Action is checked down on all streets.

At showdown, I turn up my AK first as the last aggressive actor (that's the house rule). The two players behind me table AQ and some middle connectors that missed. The big blind folds his hand face down. Middle connectors guy goes through some discussion about did I make a pair. He figures out that he didn't. During this discussion, the BB wakes up and realizes he may have made a pair and grabs his hand back. He does have a pair, he wins.

Should the dealer have mucked this hand as soon as it hit the table facedown? This wasn't an instagrab situation. The BBs cards were out there for at least 5-10 seconds.

Should the dealer wait until it is BB's turn to show down before mucking his hand as he did?