Currently, Portfolio defaults to UTC when the user does not specify a Plan Timezone, see

com.atlassian.rm.jpo.core.scheduling.load.DefaultPlanDataLoader#getPlanTimeZone

This causes some strange artefacts surrounding the sprint start times.
Example: if a sprint starts on 6 March at 10:00am (in Sydney), then Portfolio translates that to a sprint start date of 5 March.

This can be confusing, as users would expect Portfolio's out-of-box configuration to match the Jira defaults.