In the Vampire Diaries S02E21, The Sun Also Rises, when Klaus's main werewolf turns, why doesn't Klaus himself and his backup werewolf also turn at the same time?
First off, the easy one: at this point in the show, Klaus is still under the curse his mother put on him that suppresses his werewolf side. That's the whole point of the season -- Klaus's trying to break his curse. Note that, as the curse starts to break, he does start to transform into a werewolf, until Bonnie stops the spell.
As for why Tyler turned so much earlier than Jules, Klaus's witch explains this when she first brings Jules to the sacrifice. The witch has cast a spell on Jules to slow down her transformation, presumably to make it easier to handle her. (Out-of-universe, it was important that Jules be able to talk during her final scene, so she had to remain human longer.)
Even without that, though there have been indications in other cases that the older a werewolf gets, the more control they get over their transformations. Typically it's used to show that older wolves don't suffer as much from their transformations, but it also applies to their behavior, so it may well include how long you can hold the transformation off.
I think it's because werewolves turn on the full-moon night, not necessarily at the same time. The exact hour differs from person to person.