Unfortunately, there seems to be a bit of a misunderstanding around what sexism actually is: it's not sexist for something to simply not be favourable to some sample of a given sex. In order for something to be sexist it either has to make assumptions about the qualities of a given sex based only upon their gender, or be discriminatory toward a given sex based solely upon their gender. Discriminating on the basis of hours worked is the opposite of both of these.
- women are so fragile and anxious that they need someone to hold their hand through the exercises, or
- women don't have the guts to persist through studying a difficult subject?
I certainly don't believe this to be true.
If the same, fair, treatment produces different outcomes, why does that make the treatment wrong?
Now, a skew is discriminantory (by definition it is bias). Whether or not it is <sexist> is simply a question of distribution of the mechanism responsible.
Is a program of 3.5 years of self-study (lets assume, in social isolation) an equally attractive proposition? Probably not, given that women consider doing anything in isolation to somewhat socially demeaning. We know that women, for example, self-select mates based on quite the opposite: high social standing. A long self-enforced period of social isolation is thus <rationally> counter-productive from the perspective of evolutionary biology. So, if we use this as a gating function, yes we will get biased results.
Fairness is a question of expected value. A fair bet is one where the ratio of cost/benefit is equal. So, in this case where there is an asymmetric cost, the result is uneven fairness (in this sense).
Whether or not it is right or wrong depends upon your criterion for value. By one standard - maximizing the potential peformance - it would be inefficient. This is beacaus you have mean XY and below mean XX performance represented (~regardless of proportionality -- as XX is biased down in both quality and quantity). Whether or not this inefficiency is wrong or acceptable is on the whole, just re-phrasing whether or not gender bias is (or is not) wrong.
That is beyond the scope of my commentary here.
I think the literal intention of it was: "if you want to join this field, all you need to do is put in the time and effort to get really good at it". Not that you should literally lock yourself away in social isolation and speak to no other human beings for several years.
"Put in the time and effort" could also involve networking with other hackers, finding collaborators for open source project or startups, communicating on IRC channels, and learning from peers in person. Yes, there will be hours of solo grinding out code and debugging - but that's not the only thing that a programmer does.
Some people may respond to this, and some may not. Statistically, without question you will get adverse selection. So, yeah you can now start to make assumptions on how to avoid this fate, or not, but otherwise people with real options will do other things.
There are plenty of other professions, like say music, surgery, law, athletics, performance and endurance sports, teaching and many more that require a person to go outside the normal hours and work to practice, to achieve any sign of mastery. The fact that these professions demand such an work setting is not because they inherently like to discriminate against a minority, but that standards of quality are held at such a high bar you inevitable have to work that way to make a living there.
There is fundamentally nothing wrong with it.
If one offers the same thing to people regardless of their sex how can that be discriminating against them because of their sex?
Isn't this exactly why it is sexist? [1]
[1] This (being tone deaf to social cues) wouldn't work to attract women in a social setting, so why would it work in a professional one? You're basically offering up a scenario that is more likely to create anxiety for women, and as a result they will (statistcally) self-select into a different activity.