Ok take this situation. You and your friend Bob take a trip from Belfast to Liverpool and it takes you exactly one hour.
If each of you has the same operators capacity i.e. you are both PPL'ers then what happends is. You first descide who will be P1 and who will be P2
Say in this situation you are P1 your log book would look like this.
Date: 1/8/01
Aircraft: Cessna 172
Reg: G-ABCD
Captain: Self
From: EGAA (Belfast)
To: EGGP (Liverpool)
Departure: 10.00
Arrival: 11.00
Your flying time will be entered "In Command" and it will be the amout of time that you acted as pilot in command of that aircraft. So lets say you let bob fly for 10 minutes over the isle of man. then your entry would be 50 mintues "In command" and Bob's would be 10 minutes "Dual or P2" which totals 60 minutes. In Bob's log book he enters YOU as captain as you are P1.
In other words NO you cant enter the same time in a singe crew aircraft for two people.
I got all this from decoding the cryptic "Instruction of Use" in my log book. I am sure someone will correct me if I am wrong!
Happy Flying!