I need to get why SAP-FI/CO reporting transactions so often time-out on users, 
and what steps can be taken to prevent long wait times from happening.
Whether retrieving Profit Center Actual line items via transaction
KE5Z,
or running Profitability Analysis reports with KE30.

I cover PP, so not an expert on this, but the company I work for has
similar problems.  It may also depend on the way your system has been
configured.  If you run any reports on process / production orders,
ensure that they are housekept correctly.  This entails closing (CLSD
status via CORM) and flagging for deletion orders no longer required. 
These steps reduced some of our reporting times from 6 hours (& a pen
held on the enter key) to 20 mins for KK & KE transactions.