If you would like to specify a constant value for an XPath Duration (used in a wait activity or an escalation) you can follow the format specified by the w3 consortium for durations.

The lexical representation for duration is the [ISO 8601] extended format PnYn MnDTnH nMnS, where nY represents the number of years, nM the number of months, nD the number of days, ‘T’ is the date/time separator, nH the number of hours, nM the number of minutes and nS the number of seconds. The number of seconds can include decimal digits to arbitrary precision.

Weirdly enough, the duration needs to start with a ‘P’.

Also, if you are in the WebSphere Integration Developer editors, ensure that your constant is contained within single quotes.

'PT2M'

as opposed to

PT2M

The latter will cause the runtime to look for a child element named PT2M.