Message Box that auto closes

I'm using Windows 10 Enterprise, Excel/Microsoft 365 Apps for enterprise, Version 2105 (Build 14026-20246)
I'm a novice (at best) VBA user. I mostly google and borrow and modify as needed, but trying to learn too.

I have a very large Excel file with numerous tabs.
For this, I'm focused on just 2 of the tabs.

Tab 1: "Weekly Review"
Tab 2: "Weekly Pivots"
Tab 1 has 4 cells that can be changed: F1, D4, D5, K4 - these are also named cells as follows:
Fld_SelectWeeklyPullRangeType,Fld_WeekStartDateSelect,Fld_WeekEndDateSelect,Fld_SelectLatestNoOfWeeks.
Tab 1 displays 6 graphs (these are pivot graphs), these graphs are driven by the pivot tables located on Tab 2.
When any one of these 4 cell values change, I'm auto refreshing the 6 pivot tables on Tab 2.
Tab 2 will be hidden once this is fully working.

On Tab 1 I have the following code that does the auto refresh to the 6 pivot tables on Tab 2.
This code runs as expected refreshing all 6 pivots tables on Tab 2 and the graphs on Tab 1 auto update once the pivot tables are done refreshing.

Here's my current VBA code...

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During the refresh process, the mouse cursor kind of "blinks" a lot and the lower left of the screen flashes "Ready" off/on numerous times.
The refresh takes on average 10-17 seconds to complete.

What I'm wanting to do is the following so that the user is FULLY aware that the update is in process:
1. When the above code is kicked off, I would like a custom message box to appear that says "Update in process. Please do not leave this page or click any buttons. This message will automatically disappear in 15 seconds." If possible I'd like to NOT have any buttons on this pop-up (i.e. No "OK", "YES", "NO", etc).
2. I would like an auto timer for Message 1, that disappears in X seconds (I'll probably start with 15 seconds and test it several times to get this exactly where it needs to be).
3. Then I'd like a 2nd auto message that pops-up (replacing the first message) that says "Refresh is complete. Click OK to close this message." (then 1 button that says "OK" that will close the message.

I found the following code online and tried inserting it in my above code, but I broke my existing code (because I don't understand "sub" lines, where things stop and start and need inserted, etc.) The following is for only 1 message, but I thought I'd share this in case it's headed in the right direction?

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Thank you for taking a look!

Appreciate the response. I'll mention again that I'm a real novice here so...

1. I have no idea what the Application.ScreenUpdating = False is intended to do, where it gets added, why it gets added, how or why I would set it back to True, or literally anything. Would love to know more details about this.
2. The message box was helpful (to a degree). Again, being a novice, I inserted this code as shown next. So I get the Msg box for 15 seconds and the refreshing isn't occurring while the msg box is displayed on screen. I need the msg box to pop-up right away, then the refreshing is occurring for say 15 seconds, and then the msg box goes away. Also, I was also hoping to NOT have the OK button - is that possible? When I put the msg box after the refreshing then it refreshes for like 15 seconds, then the msg box pops up for 15 seconds and then it goes away.

How do I make this a seamless all in one (msg box, refreshing in background with msg box still showing, then msg box goes away)?

Sorry, here's the code as it currently sits:

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I've tried moving "parts" of the timed msg box to both sides of the refresh part of the code and this either causes it not to work at all, or it doesn't do both things, or it does them separately. I've tried numerous layouts. Here's my latest that still isn't right.

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Reaching out to see if anyone can help me wrap this up.

WBD - it works perfectly. Once again you save the day!!!! Thank you so much.