How long do user research studies tend to take when the participant needs a translator?

My team is running several user research studies on a mostly internal product with both English-speaking and non-English-speaking users. The studies are written in English.

One is a quantitative Google Forms survey with multiple choice questions. This has taken most English-speaking users 15-20 minutes to complete (internal pilot with self-reported completion time). The other is a qualitative benchmark usability study using UserTesting. This has taken English-speaking participants 15-25 minutes to complete.

Making the following assumptions:

  1. The translators are familiar with the users' domain, but not familiar with user research. (No one on our team speaks the natural languages that these users speak.)
  2. All of the studies take place remotely, not onsite. The non-English-speaking users are in different countries from us.
  3. Due to time zone differences, our team is not available to assist the participants.
  4. The product is translated into the users' languages and has the same features and a consistent layout with the English version.

How long should we tell the participants that these studies will take? Is there any research that compares how long English-speaking participants take vs. participants requiring an English translation?