GANTT: IllegalArgumentException because of constraints

Question

Testet with V1.2026.3beta 4 and V1.2026.2.

I have the following Example which does not work:

@startgantt MWE
'--- Grund‑Einstellungen ----------------------------------------------------
Project starts 2026-03-23
saturday are closed
sunday are closed
2026-04-03 to 2026-04-06 is closed
2026-05-01 is closed
2026-05-15 is closed
2026-05-25 is closed

hide resources footbox
printscale daily zoom 5

title "MEW"
footer Stand: 09.03.2026
language de
today is colored in green
'-------------------------------------------------------

[First Todo] as [a1] on {Res A} starts at 2026-03-23 and requires 1 day
[Second Todo] as [a2] on {Res A} requires 1 hour and starts at [a1]'s start
[Third Todo] as [a3] on {Res A} requires 3 days and starts at [a2]'s end

@endgantt

If I change the yellow highlighted part to start, everything works fine.

Comments

Looks like a task can only start at a day boundary and not at an hour boundary.

Is the chronology diagram (https://plantuml.com/chronology-diagram) and atlternative?

---

I think you're right that it's because of the hour. But for me, this is unexpected behavior and shouldn't be the case.

Unfortunately, the chronology diagram is unsuitable because it is no longer supported by the current release and is virtually undocumented.

---

Seems to be fixed with new ~v1.2026.3beta4 (2026-03-10 at 09:20:47 (UTC))