Yeah it can be difficult. I always had PayPal issues with Bitwine (never wanted to connect for some reason), so I didn't read much on there. Few readers list their hours on their page; however, I always checked the LAST SEEN and their LOCAL TIME. So if a psychic was seen online 13 hours ago, it's currently 10:00PM, and they're on GMT time, I'd estimate that they're online between 01:30-02PM my time. I'd always backtrack like either 30min to an hour after calculating.
Edit to Add: the notifications never worked for me. I used to have it set up for a couple in particular, but I never received anything.