JLCEL Course

CH06-L01 · applied

Timestamps and durations

Convert text to a timestamp and add a duration.

General CELRuns hereDocumented
What will I learn?

You can distinguish string, timestamp, and duration and use them in a time calculation.

Where will I try it?

Directly below, in the browser playground.

What do I do?

Run both modes, compare where their values come from, then complete the task.

Try CEL · browser pilot

Try both ways to supply values

Define local values inside one CEL expression, or provide variables as JSON input. Everything runs in your browser.

CEL pilot subset
One self-contained CEL expressioncel.bind() gives a local name to a value and returns the result of the final expression.

cel.bind()cel.bind() is an optional official extension. It is not part of the core CEL language and may not be enabled by every host application.

Tip: press Ctrl/⌘ + Enter to run.
Result

Press Run CEL to evaluate the active example.

Pilot scope: literals, explicit conversions, local cel.bind() variables, JSON variables, lists, maps, presence, collection macros, core string checks, time values, arithmetic, comparisons, logic, and the conditional operator.

What you will do

You will run the prepared expression in the playground above, change one input at a time, and explain the result. Start in CEL only, then repeat the same rule in CEL + JSON.

How it works

A timestamp is an absolute instant; a duration is an elapsed amount of time. The source value starts as an RFC 3339 string, so timestamp(start) parses it explicitly. Adding duration("2h30m") creates a new timestamp two hours and thirty minutes later.

Read the prepared example

The CEL + JSON rule is:

timestamp(start) + duration('2h30m')

Its input is:

{
  "start": "2026-07-23T08:00:00Z"
}

The CEL only tab contains the values and the rule in one expression. The enabled cel.bind() extension keeps each name local to its final argument.

Evaluation step by step

  1. The start string becomes 2026-07-23T08:00:00Z as a timestamp.
  2. The duration equals 2 hours and 30 minutes.
  3. Addition returns 2026-07-23T10:30:00Z.

Your task

  1. Run both modes.
  2. Change the duration to 45m.
  3. Enter an invalid start such as 23 July and read the parsing error.

Expected observation: A 45-minute duration returns 08:45:00Z; non-RFC-3339 text is rejected.

Common mistake

Do not add a number directly to a timestamp. Time arithmetic uses a duration, which carries a time unit.

Show the explanation

A new timestamp.

Knowledge check

What type does timestamp plus duration return?

Key takeaway

Parse external time text explicitly and perform time arithmetic with typed durations.

Sources

  • CEL-DEV — official CEL overview.
  • CEL-LANG — official CEL language definition.
  • CEL-GO-BIND — official documentation for the optional cel.bind() extension used by the self-contained tab.