update with aggregation pipeline stage

Program.cs

using MongoDB.Entities;
using MongoDB.Entities.Core;
using System;

namespace StackOverFlow
{
    public class UnitTravelHistory : Entity
    {
        public long JobDuration { get; set; }
        public DateTime Start { get; set; }
        public DateTime End { get; set; }
    }

    public static class Program
    {
        private static void Main()
        {
            new DB("test", "localhost");

            new UnitTravelHistory
            {
                Start = DateTime.UtcNow.AddDays(-1),
                End = DateTime.UtcNow
            }.Save();

            DB.Update<UnitTravelHistory>()
              .Match(_ => true)
              .WithPipelineStage("{$set:{JobDuration:{$subtract:['$End','$Start']}}}")
              .ExecutePipeline();
        }
    }
}