Successful math grad students and mathematicians, work basically all the time.
I didn't even go to lunch for about 20 years, but worked right through everyday.
i never read a novel, or watched tv. i went out to eat once a week with my family for a break, mostly for them.
there is never enugh time, if you are in competition for a grant, or to solve a big problem.
there is enough nsf grant money in math for about 1/3 of the qualified applicants, but your promotion may be based primarily on whether you have one.
of course it all depends what level you are shooting for, and who you are competing with. I was trying to be considered competitive on a national and international arena, in a difficult subject. to solve problems that some of the best people in the world were interested in. with my modest ability it required all the time i could give it.
Even a few years ago in my late 50's, when trying to rekindle my research program after a lull, i did not go out and party even on weekends, but worked everyday for several years in a row, to get back in the swing.
there is no such thing as coasting in science. you are either busting your b*tt or falling behind the leaders. the key is to enjoy it, and take only a brief time off to recuperate, without losing your edge.
as chern told me, "every now and then take off a day". the idea of taking off every weekend is absurd for real accomplishment. but i am talking about trying to be the best you can.
with this work schedule, i had the presidents fellowship as a grad student, got 3 academic jobs on graduation, including columbia, was one of 10 nsf postdoc in the US (at harvard) after 2 years, and had many international speaking invitations at conferences, visiting universities, and won several hundred thousand dollars in grants.
i noticed at harvard that fields medalists were notnoly brilliant, but they worked really hard too. the good part I learned is that hard work can really bring dividends, even with modest ability. and lax behavior is devastating, even with talent.
instead of treating work as a chore, try to become inspired, read the great thinkers, enjoy the depth of their thought and try to emulate it. be proud of hard work, and try to stay mentally in shape all the time, so as not to have to catch up after a lapse of activity.