I have a hyperthreading Pentium but find that running BOINC with two "processors" during the day slows down other applications too much despite the comments in the help file.
I would like to be able to run a project on one processor during the working day and two processors overnight but cannot see how to set my preferences to do so.

Welcome to the project, johnb.

I'm fairly sure that BOINC wasn't designed to do that.
About the only way to get more 'elbow room' is to go into preferences and set:
'Do work while computer is in use' to NO.
When you start using the computer, BOINC will stop, and start again a few minutes after you stop using it.
If you have plenty of memory, set:
'Leave applications in memory while preempted' to YES.
Otherwise cp will start again from the last 'save point'.

Les