OK, I did some practice, drove almost 100 laps and pushed Skyline to the limits. My best lap sector times weren't the fastest from all laps, so there is still a littlebit to improve (about 0,3s). So official time:
Class B:
1'05''986 MrGreen Skyline R32 V-spec II
There are few of other cars that I drove on Tsukuba, but I need to improve there's laptimes, so in couple of days I'm gonna post next results.