Yes, it's a fairly reliable indicator that things are moving - but In my experience it could still be a day or two yet, although it will often be within the next 6-8 hours, or sooner. And every indicator there is, some ewe some day will do a fortnight before she lambs, or more.
They just love to make fools of us.
If you've scanned your ewes, then I don't leave long at all with triplets. 20 mins max between lambs, then I'll be in there to assist. And usually just fetch them both out, rather than leave it for her to emit the third. If it's twins, I'd be less concerned about a delay, but would want to see some action within an hour - and it's usually nothing like that long.