On the Clock
The amount of time that it takes for a woman to reach orgasm from masturbation, sex or cunnilingus depends on her individual physiology, her emotional and mental state as she gets aroused, and of course the state of her companion, if she has one. The only thing only marker you really have on any timeline is based on how long it normally takes whenever the two of you have had sex in the past. But what if it's been ages since the last time you had sex, or if she has yet been able to orgasm during intercourse?
There are some ladies who take a long while to get where they need to be before experiencing orgasm. With such a vast number of factors involved in the process, it is a delicate juggle that may or may not line up on any given night. Some women, however, have the self-knowledge, experience, confidence and wherewithal to find their bliss in record time. Maybe she can elicit what she needs from her body just by thinking sexy thoughts, or maybe she has a partner that really knows how to get her motor running. Maybe, just maybe, your wife is one of the rare few who barely need any assistance at all! These are the women that the rest of us envy.
Many factors affect a woman's ability to orgasm, such as her mindset, where she is in her menstrual cycle, any positive or negative sexual experiences she may have experienced in the past, where and how she spent her day, how much stress she's under, even the things she has eaten or ingested including food, water, drugs, alcohol and/or medications. Some of these things will affect her positively - fond memories from a smell or a touch can send her right into sexy space, or small amounts of booze might help her to loosen up when she's feeling anxious. Others, like fatty foods, excess alcohol and many prescription medications, will only serve to dampen her sexual fire.
Ask your lady if she masturbates and experiences orgasm on her own. If she does, she's likely to orgasm during sexual intercourse far more easily than her non-masturbatory counterparts. Don't bother asking her how long she takes as an indicator of how long it'll take while you're inside of her though; like you when you touch your own cock, she knows her body so well that masturbation will get her to climax consistently much faster than any other method.
What will help to move things along is extended foreplay before penetrative intercourse – fingering and oral sex are sure to get her nice and warm before penetration. You'll get her that much further along the path to climax this way, so that her juices are revved and ready to go when you make the transition from foreplay to intercourse. Ask her to show you what she does on her own, or what angles, pressure and rhythm she really enjoys. If you can get to know what gets her off solo, you'll be that much closer to learning what really makes her tick.
All of this information doesn't truly answer the question though, does it? I'm not avoiding it, I promise. I just want to ensure that you understand all of the factors involved before you start checking the clock and timing your lover's orgasmic process. In a nutshell, most women take anywhere from ten to thirty minutes to achieve orgasm during penetrative sex. That time frame doesn't include foreplay or aftercare, but rather direct clitoral head stimulation or G-Spot play during intercourse.