How to define scriptmanager timeout property in custom master page

Question

I have a custom master page. When you create a custom master page then another page with similar name is automatically created by SharePoint. For e.g. my master page name was mymaster.html so sharepoint created mymaster.master file with it. I want to increase the AsyncPostBackTimeout property of ScriptManager. I opened mymaster.html in SPD but didn't find any code there. Then I opened mymaster.master in SPD and I can see the ScriptManager code written as below.

<asp:ScriptManager id="ScriptManager" runat="server" --more code here-- />

Problem is, SPD doesn't allow you to edit .master page and I can't add this code in my .html master page file. How to edit this code in SPD?

Answer 1

How to customize master pages in SharePoint 2013

In SharePoint 2013, if the master page, for example, oslo.master is associated with a html page, i.e., oslo.html, you cannot edit the .master page directly. You should edit the html page with your favorite html editor(for example, Visual Studio), find the right place to insert your tag. SharePoint will automatically synchronize your change to the .html file to the .master.

For more information follow this thread

From another hand, in order to edit master page directly, the association with html page should be broken (SharePoint 2010 mode).

Below is demonstrated how to break the master page association and customize master page file.

Example

1) Open master page Olso.master in Edit mode

2) Select Save as action to save it as a custom master page, let's name it, lets say, helsinki.master (Note: helsinki.master is not associated with html page, it means it could be edited directly )

3) Open helsinki.master and find asp:ScriptManager control

4) And finally, specify properties for asp:ScriptManager control and save the changes