I started transition by jumping straight into HRT. And my plan from the very beginning was "once I start passing as female consistently, and I believe a reasonable person looking at me could accept me as female, that's when I'll go full-time."
When I first went on full-dose HRT in January of 2013, judging by other people's timelines on Youtube I was expecting that I'd be full-time by the end of the summer. But the summer came and went, and by the 7-month mark on HRT, not only was I not full-time, but I'd never even come close to being gendered female for the first time. And looking back, I still looked completely like a guy. (Except with a wig on. With the wig, I did wear blatantly-female clothes, and I was gendered female, but I was still stared at a lot, still got rude comments from people, plus I didn't want to be forced to rely on a wig in order to pass anyway.)
It took another 3 months after that before I finally started looking somewhat female-ish to myself when I looked in the mirror. So I switched over to androgynous clothes, and people started getting confused, and asking me whether I was a boy or a girl. But I still didn't get my first ever wigless female gendering until the 11.5-month mark on HRT.
At 13 months, I was finally starting to get the courage to move on from my androgynous wardrobe and go out in blatantly-female clothes. However, the first three times I did so, I was stared at, and even told by a random stranger during one of those times "if my kids went out like that, I'd slap them." But despite that, I was getting gendered both male and female pretty consistently just in my normal daily outfits. I even started "male fail"ing on occassion, being gendered female even when I was wearing male clothes.
At the 14-month mark, I FINALLY found a look that I felt worked for me... ponytail, earrings, and female clothes. And so I started going out that way. And miraculously, at long last, everyone started gendering me female, and the stares slowly stopped. I started using the women's room (without incident, thank God,) and for the most part started being able to be pretty sure that I really was passing.
It was at almost exactly the 15-month mark that I finally officially went full-time, sending in my legal gender-change forms, getting the ball rolling on my name-change, and wearing blatantly-female clothes without too much worry and without incident. It took me that long to be confident that I was passable enough. I probably could have done it a couple of months earlier, but I'm a very cautious person. And I still honestly have doubts about whether I really am passing or not, but real-world evidence has proven me wrong enough by now that I can finally get my self-critical mind to shut up more often than not.
The thing is, it took me TWICE as long as I originally thought it was going to. I was expecting to start being misgendered by the 6-month mark. It took until almost 12. I was expecting to look female enough to go full-time by the 7-8 month mark. It ended up taking until 14-15. So if there's anything I've learned, it's that transition goes at its own pace, and you'll save yourself a lot of grief and agony by just letting it happen and not worrying about when it happened for others. I had a complete mental MELTDOWN at the 10-11 month mark because every single one of my friends was full-time by that point, where I'd still never even been gendered female for the first time.
The 2-year mark is when people say that you can finally start making assumptions about what you'll eventually look like. Until then, you can and will keep feminizing, so don't lose hope!