How to assign lastUpdate to an item?

[Udo_Hartmann]

If talking about Time and Date, please take a look at

DateTime Conversion (openHAB 2.x)

Because openHAB 3.x rules now use Java Time API instead of Jodatime, there is a new DateTime Conversion thread for openHAB 3.x. Overview In openHab 2.x there are different ways to handle Date/Time values. DateTimeType A DateTime Item carries a DateTimeType. Joda DateTime By default openHAB 2.x-Rules use a Joda DateTime class to represent time, most notably now. Epoch The lowest common denominator when working with time is to get at the epoc value. Epoc is the number of milliseconds …

There are some other really good tutorials for Type conversion.
Maybe also interesting:

Design Pattern: Simple State Machine (e.g. Time Of Day)

Edit: OH 4 Updates Problem Statement Often in home automation there is a need to track certain states that the system is in. Events occur to transition from one state to another state (e.g. at noon we transition to the AFTERNOON state). The collection of all the possible states and the transitions between events is called a “state machine”. This design pattern illustrates some ways OH can implement very simple state machines. One of the most common uses of a state machine like this is to trac…