Completing Set (O) Form, Section 6 Immigration History.

[zeeshop]

I am filling set (O) form and applying ILR on 10 years basis.

I went abroad on holidays five times during my stay, each of my trip was less then 2 weeks.
But in my european visits there is no exit stamps and no entry stamp on passports, and I dont have exact dates. can I just fill dates which remember by memories.
Please advise in this matter, if I fill approximate date should I also mention that these return dates may be one or two days up and down.

Thanks and regards.
Zee