Hi there akajezebel,
If the time on reminders on your iPhone is not accurate, let's first ensure that the time of your iPhone is set automatically using these steps from Change the date and time on iPhone since that can cause this issue to occur:
1. Go to Settings
> General > Date & Time.
2. Turn on any of the following:
* Set Automatically: iPhone gets the correct time over the network and updates it for the time zone you’re in. Some networks don’t support network time, so in some countries or regions, iPhone may not be able to automatically determine the local time.
Let's also check for any available iOS updates since this can install bug fixes that can resolve unexpected issues like this. This article shows how to back up and update: Update your iPhone or iPad
If this continues after checking your date and time settings and updating your iPhone, please provide more details on if this happens with new reminders as well so that we can isolate this further.
Cheers!