time: the first 1000 feet after the exit is about 10 sec (because you will speed up from about 80mph to 120mph. The every 1000 feet after that will take about 5.5 sec. so if you jump from 14000 and open parachute at 6000, your freefall time is about 50 sec. However, experience jumpers usually open our parachute at 3500, so we got more freefall time (about a minute).
instructor: sometimes students forgot to pull, instructor will try their best to pull the parachute for them (however, students are still responsible for their own skydives). The first couple of jumps, students need to show the instructor they know how to do it right. and also able to be stable during freefall. (sometimes it's hard to tell how hard the instructor is holding on to the student from the video)
The little chute is called drogue. The parachute can only be safely deployed during certain speed and the tandem pair is usually fall way faster than a single person (about same surface, but double the weight). The function is to slow the tandem pair down to normal freefall speed to make sure the parachute won't open too hard and you got more freefall time as well.
世界就是我的跳傘場! The World Is a Drop Zone