Yes, "kalahating oras" is "half an hour", but the "isa" and the "- isa't (isa at)" before the phrase add the "one to one" meaning to it.
The translation of that sentence would be:
Ito, ‘yun ganitong size (sa) tantya ko, mga isa - isa’t kalahating oras ‘to, pare. = This, one of this size, in my estimate, this will take about one to one-and-a-half hours, buddy.
Note:
1. There should be a “sa (in)” before “tantya ko (my estimate)” had he not paused between “size” and “tantya”. To us, that pause is like a silent “sa”.
2. I added “this will take” in the translation to apply the “ ‘to/ito ” that appeared after “oras”.