"it's time that we left"?

[dihen]

Which ones are acceptable? And are there any differences in meaning?
`
"it's time that we left"
"it's time that we leave"
"it's time that we should leave" (is this incorrect?)
"it's time for us to leave"

[Tdol]

"it's time that we left"
"it's time that we leave" , though you will find occasional examples where people use the present
"it's time that we should leave" (is this incorrect?) I wouldn't say incorrect, but wouldn't use it
"it's time for us to leave"

[dihen]

I thought it was usually possible to replace the "for [object] to [verb]" form with the "that [subject] [present subjunctive verb]" form, but it's not?

[Tdol]

It's not incorrect, but you don't hear it used as much as the others.