# Isodatetime: get Most most T0600Z before current Cycle Point

**URL:** <https://cylc.discourse.group/t/isodatetime-get-most-most-t0600z-before-current-cycle-point/1333>\
**Category:** Cylc Development\
**Created:** [July 27, 2026, 1:18pm UTC](https://cylc.discourse.group/t/isodatetime-get-most-most-t0600z-before-current-cycle-point/1333 "2026-07-27T13:18:57Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![wxtim](https://yyz2.discourse-cdn.com/free1/user_avatar/cylc.discourse.group/wxtim/32/151_2.png) [@wxtim](https://cylc.discourse.group/u/wxtim)\
**Post date:** [July 27, 2026, 1:18pm UTC](https://cylc.discourse.group/t/isodatetime-get-most-most-t0600z-before-current-cycle-point/1333/1 "2026-07-27T13:18:57Z")

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I’m trying to work out if there is a nice way of doing

| Task Cycle Point | Required Cycle Point |
| --- | --- |
| 1200 | 0600 today |
| 1800 | 0600 today |
| 0000 | 0600 yesterday |
| 0600 | 0600 yesterday |

I was hoping for something similar to the `previous(T06)` from the Cylc config, but that’s in the config layer. Any magic?

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**Author:** ![oliver.sanders](https://yyz2.discourse-cdn.com/free1/user_avatar/cylc.discourse.group/oliver.sanders/32/110_2.png) [@oliver.sanders](https://cylc.discourse.group/u/oliver.sanders)\
**Post date:** [July 28, 2026, 10:47am UTC](https://cylc.discourse.group/t/isodatetime-get-most-most-t0600z-before-current-cycle-point/1333/2 "2026-07-28T10:47:31Z")

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If I’m understanding correctly, that’s:

```auto
T06 = a

T00 = a[-PT18H] => b
T06 = a[-PT24H] => b
T12 = a[-PT6H] => b
T18 = a[-PT12H] => b

```

  

It is often the case that these “targetted” dependencies are collapsed is via the dependent tasks themselves, e.g:

```auto
T06 = a

T06 = a[-PT24H] => b

T00, T12, T18 = b[-PT6H]:succeeded => b # (or replace :succeeded with :started)

```

Though this may or may not be appropriate.

  

But beyond that, there is no `previous(...)` syntax supported in inter-cycle dependencies at present.

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**Author:** ![MetRonnie](https://yyz2.discourse-cdn.com/free1/user_avatar/cylc.discourse.group/metronnie/32/125_2.png) [@MetRonnie](https://cylc.discourse.group/u/MetRonnie)\
**Post date:** [August 4, 2026, 10:46am UTC](https://cylc.discourse.group/t/isodatetime-get-most-most-t0600z-before-current-cycle-point/1333/3 "2026-08-04T10:46:39Z")

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I proposed that as a possible solution for relative inter-cycle dependencies: [Relative Inter Cycle Dependencies · Issue #2452 · cylc/cylc-flow · GitHub](https://github.com/cylc/cylc-flow/issues/2452#issuecomment-2823983310)