When the document is opened for the first time it loads the document into RAM on the server and should be quicker for all subsequent users who open it (subject to document timeout settings). You can improve the first opening by pre-loading the document in QMC (Document > Server > Performance). So if you reload at 6am, set the preload and have a timeout of 480 minutes (8hrs), it will reside in memory until 2pm if nobody opens it. (There are a number of places to set the document timeout (System > Setup > Server > Documents and in the performance area above).
If it's a problem for every time someone uses it then you either need to optimize the document or improve the server spec.. Try searching for server optimization documents on here.
some tips to improve the document performance..
1. Don't load the historical data. I mean load the data for last 5-7 years as per the user requirement.
2. Do all possible calculations in script it self.
3. Minimize the objects which are not necessary at first look.
4. On opening the document, restrict the data to latest 3 years.
5. Drop the unnecessary fields from the data model.
Analyze the document performance, by using Document analyzer, it will give you which object taking more time.