Believe it or not, when you schedule a date matters. If you aren't sure when, follow the 8PM rule: schedule your dates for 8pm. Here are a few reasons why 8PM is often the ideal time for a date.
1. It's in the evening.
I have written about this a few times, such as in my article: 6 Reasons Why "Day Dates" Are A Bad Idea.
Don't bother with things like coffee dates during the day. If you want to meet a girl, make sure you are meeting her in the evening or at night. There are a myriad of benefits including societal association of night time and darkness, more date options where you can be close to each other, and usually no plans after the date so there is nothing stopping a good date from continuing well into the night.
2. It blocks other plans
I hinted at this at the end of (1). One of the last things you want to do when scheduling a date is scheduling one that has a hard cut off time (due to you or her). It is easy enough to end a date, you don't need a real activity to follow in order to end it. What is much harder to do is have a really good date, and you really don't want to have to cut off a good date short because you scheduled a date at a time you or she had a prior commitment. It isn't always easy to know if a woman is double booking her night, but if you propose an 8PM date, you make it much harder to do so.
3. It's not too early and not too late.
8PM isn't really a hard rule, but it is a nice time that I find fits the true essence of this rule: scheduling a date at a time that is "not too early" but also "not too late". At 8pm, if someone agrees, it is highly unlikely she will make firm plans for later unless it is the weekend (point 2). Furthermore, 8pm is a time that leaves everything on the table in terms of night time activities. If you don't want to take her to dinner it's late enough it is expected she will have already eaten. If you want to eat, 8pm isn't too late for dinner. Just about every night time venue or activity is open at 8pm with time to spare, and public transportation (if relevant) usually is readily available. In other words, 8pm is not too early, and not too late.
3(a). The night isn't over if the date is bad.
A corollary of (3) is that if the date is bad, it will likely be over by 9pm or so which still gives you plenty of time to enjoy the night. Whether you use that time to catch up on some TV shows, go out with your friends after, grab a late bite, or even call your friends with benefit to come over! Not too early and not too late is very valuable.
3(b). If the date is good, it's not too late
If a date is going well, you can probably leave the first venue after around 2-2.5 hours. At this stage, it is only 10pm or 10:30pm, which makes it likely not late enough to call it a night. See if she wants to come over to your place or hang out more somewhere. It likely won't be late enough that she says no. Though note, even if she says no, it doesn't mean the date was not a success.
4. It forces commitment from her part
As I mentioned in (2), 8pm is a time that likely blocks off other plans from her night. This means that if she agrees to meet you at 8pm, she is making a commitment. When women invest in you, they also end up putting in more effort to ensure things go well. You want her actively trying to enjoy the date versus if you schedule a date at a very convenient time for her, she could just treat the date like a "free option" and only really engage if she is instantly smitten by you.
5. It gives her (and you) time to unwind
8PM is usually a good time because it is not right after work for most people. This gives each of you time to relax, unwind, hit the gym, or get a few things done to clear out the rest of your night. Sometimes, meeting a woman straight after a long day at work will lead to her acting anemic. Give her (and yourself) time to recharge after the work day so you both are more energized to go out.
It's not a hard and fast rule
An 8PM isn't a hard and fast rule, but think about the reasons why I like an 8PM date and try to schedule your dates in such a way that they hit all 5 elements I discussed above. For example, if your date works from 6am to 4pm, it makes sense to schedule a date on the earlier side so that it will be harder for her to use "I have to get up early to get to work" as an excuse to not hang out longer.