Cold start issue (only occurs when sat overnight)

[AllHailKingVolvo]

Hi all,
My Torslanda (B200F) has developed an odd starting issue, when it's been sat overnight it will often take prolonged cranking to get it to fire up. Sometimes 20-30 seconds. Once started, it will run perfectly all day and stop/start faultlessly.

I suspect a fuel issue, I haven't changed the fuel filter or underbody pump since I've owned it and I'm curious as to whether it might be suffering from a partial blockage or weak pump which means the car is struggling to make sufficient pressure at the rail for the first start of the day.

Does that sound right, or am I barking up the wrong tree? I've had hot starting issues with the B200F in my 744 which were cured by changing the coolant temperature sensor. Could that be the cause of this issue, despite the problem being the other end of the temperature scale?

I'm keen to diagnose it properly rather than fire the parts cannon at the car as money is a bit tight at the min. Huge thanks in advance for any and all help!