i could be wrong, but i don’t think there’s a great way to offset a bunch of observations by an hour after they’ve been loaded, unless you’re comfortable using the API. there is a batch edit screen (https://www.inaturalist.org/observations/edit) that allows you to update multiple observations, but i think if you use this, you’d either have to set all items in a given set to the same date/time, or else you’d still have to change the times one record at a time (although multiple changes could be saved together).
although it is possible to filter for observations that you loaded using the iOS app (https://www.inaturalist.org/observations?user_id=arvel&verifiable=any&oauth_application_id=3), i don’t think there’s an easy way to get only observations loaded via the web.
so then the only way that i think you can achieve what you’re describing is to adapt the workflow described in https://forum.inaturalist.org/t/batch-updating-location-accuracy/11421. when you export the observations, make sure you include oauth_application_id as one of the fields to be exported. when you get the results from the CSV, look for records where the oauth_application_id is blank. these will be the observations you loaded via the web uploader.
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that said, in most cases, i don’t think it’s terrible that observations are off by an hour. there are lots of observations that have the wrong time loaded in the system for various reasons. so if some of yours are off, they have lots of company.