Visual Studio C# delay function for if statment

I'm looking for a way to create a delay in my code without stopping the rest of the code in this time frame. It has to work as follows. If a condition is true for X amount of seconds, set the alarm bool High. The code below is a part of code where I set the alarms but there needs to be a delay.

I'm very new to C# so try to dumb it down a bit, maybe a small example or links.
I also check there but i cant understand some things: https://www.plcnext.help/te/Programming/Csharp/Csharp_in_PLCnext.htmmehndi

if (Valve.Parameter.NormallyOpen == false)
{
if (Valve.Status.Output == true & Valve.Status.Opened == false)
{
Valve.Alarm.NotOpened = true;
}

if (Valve.Status.Output == false & Valve.Status.Closed == false)
{
Valve.Alarm.NotClosed = true;
}
}
Some background info: this will be a valve control block in PLCNext written in C#. The control block should give a alarm if the valve is send open but does not give open feedback within X seconds (takes time to open).

using System;
using System.Threading;
using System.Iec61131Lib;
using Iec61131.Engineering.Prototypes.Types;
using Iec61131.Engineering.Prototypes.Variables;
using Iec61131.Engineering.Prototypes.Methods;
using Iec61131.Engineering.Prototypes.Common;

namespace EclrFirmwareLibrary1
{
[FunctionBlock]
public class Valve_Test
{
[InOut]
public Valve Valve;

[Output]
public bool Output;

double seconds = 1.00; // 1 Second Interval


[Initialization]
public void __Init()
{
//
// TODO: Initialize the variables of the function block here
//
}

[Execution]
public void __Process()
{
Valve.Status.Interlock = Valve.Control.Interlock;
Valve.Status.Opened = Valve.Control.FB_Open;
Valve.Status.Closed = Valve.Control.FB_Closed;

if (Valve.Control.Manual_Mode == true){
Valve.Status.Manual_Mode = true;
Valve.Status.Auto_Mode = false;
}
if (Valve.Control.Auto_Mode == true & Valve.Control.Manual_Mode == false){
Valve.Status.Manual_Mode = false;
Valve.Status.Auto_Mode = true;
}

if(Valve.Status.Interlock == false & Valve.Alarm.General == false)
{
if (Valve.Status.Manual_Mode & Valve.Control.Manual_Control)
{
Output = true;
Valve.Status.Output = true;
}
else if (Valve.Status.Auto_Mode & Valve.Control.Auto_Control)
{
Output = true;
Valve.Status.Output = true;
}
else
{
Output = false;
Valve.Status.Output = false;
}
}
else
{
Output = false;
Valve.Status.Output = false;
}

//Alarms

---

var startTimeSpan = TimeSpan.Zero;
var periodTimeSpan = TimeSpan.FromSeconds(seconds);

var timer = new System.Threading.Timer((e) =>
{
CheckValve();
}, null, startTimeSpan, periodTimeSpan);

}

private void CheckValve()
{
if (Valve.Parameter.NormallyOpen == false)
{
if (Valve.Status.Output == true & Valve.Status.Opened == false)
{
Valve.Alarm.NotOpened = true;
}

if (Valve.Status.Output == false & Valve.Status.Closed == false)
{
Valve.Alarm.NotClosed = true;
}
}
else
{
if (Valve.Status.Output == false & Valve.Status.Opened == false)
{
Valve.Alarm.NotOpened = true;
}
if (Valve.Status.Output == true & Valve.Status.Closed == false)
{
Valve.Alarm.NotClosed = true;
}
}

if (Valve.Status.Opened == true & Valve.Status.Closed == true)
{
Valve.Alarm.OpenedAndClosed = true;
}


if (Valve.Alarm.NotClosed || Valve.Alarm.NotOpened || Valve.Alarm.OpenedAndClosed)
{
Valve.Alarm.General = true;
}
}

}
}