Are these drawn onto reference? They look very good to me, although some of those cylinders could have taken more time (the right most one from the bottom left batch sticks out to me for example).
As far as gesture drawing goes, the top left batch is a little to simplistic in my oppinion. For 30 seconds I'd aim to get closer to the top right ones.
I'd recommend writing a bit more about what it is you practiced (time constraints if there were any, use of reference). Makes it easier to give applicable and usefull criticism.
Just from what I see I'd say you did great.