Hi:
From the outset.
You can see recent and emerging peduncles link below.
All of them bloom this spring/summer twice.

Here is a link that might be useful: peduncles

It depends on the Hoya and other variables, but the duration can range from one to several months.

Examples:

Here, Kelly's H. burmanica took two months

In the last thread, Pug mentions her H. imperialis is budding up (04.06.2011) and she finally posts pictures of it in full bloom later that month (04.23.2011)

Cindy's elliptica took 2 months as well, falling almost on the same timeline as Kelly's burmanica