iCal: time displayed on TRMNL and time displayed on previews are different when trying to offset times

[ymstnt]

I'm trying to use the built in iCal parser to display events from various calendars.

I have two calendars with different timestamp methods. One has the timezone offset set correctly, the other one uses UTC (+0:00), like so:

{
    ...
    "SUMMARY": "Event1",
    "DTSTART": "2026-04-30T11:00:00+02:00",
    "DTEND": "2026-04-30T12:00:00+02:00",
    "SEQUENCE": "0",
    "STATUS": "CONFIRMED"
},

and

{
      ...
      "SUMMARY": "Event2",
      "DTSTART": "2026-04-30T12:25:00+00:00",
      "DTEND": "2026-04-30T14:05:00+00:00",
      "SEQUENCE": "0",
},

The display as expected in the preview and on the TRMNL device itself, the events with +2:00 offsets display correctly and the events with +0:00 display incorrectly:

(For simplicity, the green events are from calendars with correct offsets, the red ones are ones from the calendar with the incorrect offset (UTC, +0:00) and the black boxes are not related)

So naturally, I tried to fix the offset by using event.DTSTART | date: '%s' | plus: trmnl.user.utc_offset | date: '%H:%M' as per TRMNL's official article about liquid and timezones. This is when things started getting weird.

In the preview window, it looks like, this have had the intended effect. Events from both calendars are correctly displayed using the +2:00 offset now:

(Again, the green boxes are from the calendars that were correct even before the change, and the red ones are the ones with the incorrect offset, which are now offset correctly to +2:00)

However, on the TRMNL hardware itself, they are displayed completely differently:

I kinda get that the "correct" calendars get the +2:00 offset and it's displayed incorrectly because of that. However, I don't get that why the "incorrect" calendar suddenly gets a +4:00 offset, even though without the trmnl.user.utc_offset it had no offset at all.

This doesn't seem to only happen when using trmn.user.utc_offset. On a previous calendar plugin attempt, I didn't know of this feature and it still happened. There I simply added + 2 hours to the time.

I'm using LaraPaper 0.34.0, with TRMNL FW1.6.10 on a SeedStudio 7.5" OG TRMNL kit.

[bnussbau]

Do you have APP_TIMEZONE set in your docker-compose configuration? If so, UTC is recommended.

It's possible that removing the environment variable (or setting to UTC) fixes the issue, if you're setting your timezone in the profile settings instead.

[ymstnt]

I didn't have that env variable, setting it to UTC made no difference.

[bnussbau]

Could you recheck with 0.34.1?

[ymstnt]

Could you recheck with 0.34.1?

Checked it, same issue unfortunately:

Correct calendars still get +2:00 offset, incorrect calendars get +4:00 offset with plus: trmnl.user.utc_offset, but only on the display itself, preview is still fine.

[ymstnt]

I've kept trying and the following results in the desired effect:
{% assign st = event.DTSTART | date: '%s' | date: '%H:%M' %}

The date: %s part is what converts the date into a unix timestamp and strips them of any UTC offsets.

In larapaper's preview, this is reflected correctly. My calendar with the correct offsets displays weird times (like + 6 hours and -2 hours, because those are the offsets defined) and the calendar with no offsets displays the same as without that part.

However, for some weird and unknown reason, the TRMNL display still adds my own offset (set in larapaper's Timezone Settings), but only if I add the date: '%s' part.
So the display actually shows the correct (desired) times for both calendars now. It still means the preview and what's actually shown are not on par with eachother. I'm not sure if this is an issue in TRMNL's 1.6.10 firmware, how it interacts with this particular device or in larapaper, or how that interacts with this firmware/device.

[ymstnt]

Hmmm, I just also noticed, on the Dashboard page, the preview thing shows EXACTLY what's on my TRMNL display. So it shows the correct dates as well (by that I mean with the display's weird built-in offset). Only the Preview button on the plugin's page shows different dates.