How to write a hour & minute-selector

I want to add a starting time and end time in my application model, using a dropdown selector to choose the hour (24h) and minute.

Can you help me model this, including the appropriate numerical-types?

This does not exactly answer your question because you explicitly mentioned dropdown selectors, but it is a solution to allow input of a time between 00:00 and 23:59:

//...

root {
	'Start 1': number positive 'seconds' @min: 0 @max: 86399
	'Start 2': number positive 'minutes' @min: 0 @max: 1439
}

numerical-types
	'seconds' @duration: seconds
	'minutes' @duration: minutes
	'hours' @duration: hours

It shows like this in a generated client, including validation:

If it really has to be a dropdown then you could use two stategroups with separate states for all hours and minutes of the day, like this:

'Start': stategroup (
	'00' { }
	'01' { }
	'02' { }
	'03' { }
	'04' { }
	'05' { }
	'06' { }
	'07' { }
	'08' { }
	'09' { }
	'10' { }
	'11' { }
	'12' { }
	// etc.
)

Then you would get this:

However the disadvantage is that this makes it hard to perform any kind of numerical calculation based on the entered values.

Alright, so as of today there isn’t a GUI annotation or something to only change the visualization into a dropdown selector. Thanks for the clarification!

Also be careful using these values in a calculation. Date and date-time values are stored in UTC, but are displayed in the user local timezone.