In reply to Pete-West88:
I would be very, very cautious if you're experiencing any elbow pain and would suggest backing off that hold immediately. Search this site for elbows and you'll see how they can turn into a long-term inflammation and hold you back a lot more than relative weakness on the 35s.
There was a good recent article on UKC for antagonist exercises for elbows - worth searching it out and doing some of them as precautionary measures.
Fingerboarding is highly repetitive so if your arm position is wrong or tweaking your tendons, it will do it repeatedly.
Twice a week maybe seems a bit much if it's your first experience of fingerboarding. Maybe you've been building up too fast, even though your perception is that it's gradual. Back off to once a week, make sure you only do a few weeks at a time. Fingerboard for a few weeks, climb normally for a while, fingerboard again.
Don't want to be overly negative, but you definitely want to avoid any elbow problems. Listen to your body or you end up plagued with injuries like me and lots of other climbers I know!