Error in Power Query combining overlapping start end datetime fields

You can try this Power Query code, which seems to be a bit faster:

let

//Change next line to reflect actual data source
    Source = Sheet1,
    // Sort by StartDate, then EndDate
    Sorted = Table.Sort(Source,{{"Start", Order.Ascending}, {"End", Order.Ascending}}),
    
    // Add index
    Indexed = Table.AddIndexColumn(Sorted, "Index", 0, 1),
    
    // Group and merge overlapping ranges
    Grouped = Table.Group(Indexed, {"ID"}, 
        {{"Merged", (t) =>
            List.Accumulate(
                Table.ToRecords(t),
                {},
                (state, current) =>
                    if List.IsEmpty(state) then
                        {[Start = current[Start], End = current[End]]}
                    else
                        let
                            last = List.Last(state),
                            remaining = List.RemoveLastN(state, 1)
                        in
                            if current[Start] <= last[End] then
                                remaining & {[Start = last[Start], 
                                             End = List.Max({last[End], current[End]})]}
                            else
                                state & {[Start = current[Start], End = current[End]]}
            )
        , type table[Start=datetime, End=datetime]}}
    ),
    
    Expanded = Table.ExpandTableColumn(Grouped, "Merged", {"Start", "End"})
in
    Expanded

In VBA, Application.ScreenUpdating = False will disable writing while the macro is being executed. But if you do the entire logic within VBA, that wouldn't be necessary. But for large data sets, I would think Power Query would be faster for a number of reasons.