In case you are wondering when to use "i", "om", or "på" en timme:
- i en timme = lasting for a duration of an hour, as in "we'll stay for an hour"
- om en timme = in an hour, as in "we'll leave in an hour"
Those are simple. på en timme means that something will take an hour to accomplish. For instance: vi kan flyga dit på tre timmar = (literally) we can fly there in three hours = (idiomatically) it takes us three hours to fly there.
It's also used for negating durations. For instance:
- När kommer du? (When are you coming?)
- Om en timme! (In an hour!), or
- Inte på en timme! (Not in an hour!)
The forvo guy seems to pronounce "gym" the English way (≈ like "Jim" as you said). It's normal to pronounce it the Swedish way and TTS is ok here. You can compare to and pick the first part of