Go to Account settings from the profile picture menu in the desktop version of iNaturalist to set a time zone. I found that my observations being posted using the Android app were showing as being 17 hours old as soon as I uploaded them. Although my Moto G7 phone was set to Central Daylight Time here in Wisconsin, the desktop account settings were still set to GMT+11 which is where I live and work. I am at GMT-6 for only this summer. The mobile app in Android uses the time set in the desktop version, not the time zone set on the phone.
There may be way to set a time zone in the desktop app per each observation, but not in the mobile app as far as I am aware.