I've set a reminder through Gemini, then tried to change its time. Told me there are no active reminders to change. Created another reminder with correct time. Got both reminders.
I said "Hey Google instead of reminding me about the bananas on Tuesday, remind me on Wednesday" and that worked. It's quite possible these things only work on Android 15 QPR 1, or only on a Pixel Pro, or who knows. Its capabilities have noticeably expanded in the last few months. One thing I know it still can't do, that the old Assistant did, is control a Sonos.
ETA: The joke is I don't even have Google Tasks installed, so I am not sure what effect those Tasks items would have. They might only surface on the side pane of Gmail.