Dynamically evaluate Duration

[ChemEnger]

I would like to dynamically evaluate hours or minutes from durations.  I have successfully used a 'dictionary' table to describe data types in a master data table, e.g.

Column Name	Type	Units
Start Date	type date
Temperature	type number	°C
Pressure	type number	barg
Long Duration	type duration	hours
Short Duration	type duration	minutes
Comments	type text

I can then use

#"Added Evalaution" = Table.AddColumn(<Dictionary>, "Evaluate", each Expression.Evaluate(Record.Field(_, "Type")))

and

#"List of Transforms" = Table.ToRows(#"Added Evaluation")

to generate a list that can then be passed to

#"Changed Types" = Table.TransformColumns(<Master>, #"List of Transforms")

This will dynamically change the column types based on the 'Type' column in the dictionary.

What I would now like to do is dynamically take the 'hours' and 'minutes' from the units column (converted to 'Duration.TotalHours' and 'Duration.TotalMinutes' as strings) and use them as a transform function.  I have tried

#"Added Duration Evaluation" = Table.AddColumn(#"Previous Step", "Duration", each Expression.Evaluate(Record.Field(_, "Units")))
z

But I get the error "Expression.Error: [1,1-1,20] The name 'Duration.TotalHours' doesn't exist in the current context".

Specifically, I need this to run in the service, not desktop, and I want to chart the numbers with human-readable values so I can't just use duration data types.

Edit 1: I know I can brute force it by multiplying my duration (which is essentially a fraction of a day) by either 24 for hours or 24*60 for minutes but I think I'd have to stuff this in a loop of columns and it's not very elegant

Edit 2: Not perfect but I have taken the approach described in Power Query: Data Transformation of Dynamic Columns

// Transform those columns flagged as hours to Duration.TotalHours
Hours = Table.TransformColumns ( 
    #"Changed Types", 
    List.Transform ( 
        Table.SelectRows(<dictionary>, each [Units] = "hours")[Column Name], 
        each {_, Duration.TotalHours, type number}
    )
)

And of course, the same for [Units] = "minutes" to Duration.TotalMinutes

[lbendlin]

But I get the error "Expression.Error: [1,1-1,20] The name 'Duration.TotalHours' doesn't exist in the current context".

Add it to the context as requested.  There is an additional parameter to Expression.Evaluate().

Expression.Evaluate(Record.Field(_, "Units",[Duration.TotalHours=Duration.TotalHours])