I'm not sure which page you are refering to.
In the picture, you show a drafting default, shich I believe flies out a browser in the resource bar. I am not familiar with that.
I am familiar with the general NX Welcome Page Duration, which is set in Gateway > User Interface > Options. For this one, we set the default to 30, but you can enter 99999. There are 2 reasons for the low number - we don't think new users need it after some experience, and it uses a lot of memory when NX starts up, so we want to reduce the resources.