My impression is that
was never contracts. I would take
When's the last time... as
When is the last time ... -- I
think.
Forms of
do do contract after question words in
very casual conversation (
's, 'd). The
'd seems to me more common and more natural sounding than the
's. I placed question marks before the sentences below that don't strike me as the best choices. (Personal opinion.)
Where'd he go on vacation? [wair dee]
??Where's he go on vacation? [wair zee]
?When'd he leave? [wen dee]
??When's he leave? [wen zee]
How'd he find out? [howdee]
???How's he find out? [howzee]
Why'd he do
that? [widee]
???Why's he do
that? [wizee]
Who'd he think'd do it? [hoodee]
?Who's he think'll do it? [hoozee]
???What'd he say? [wuddidee] [wuddee]
?What's he say? [wutsee]
CJ