How long is a piece of string?
It comes with practice. I've only got two weeks on snow behind me, plus a year as a member of our dry slope in between. I can do parallel on gentler terrain, but when it becomes steeper. I revert back to slow, controlled snowplough turns.
My DH enjoys skiing but is the least confident in our group. On our holiday at Christmas, he was quite content to only ski half days and spend the other half relaxing by the pool or in the apartment. The DC and I skied considerably more (they were in full day ski school anyway).
I'd say day four of your very first holiday. You're about right, to be honest.
For us, it was day 3 that we felt as you do. We'd booked a private instructor for private lessons on the Sunday, Monday, and Tuesday mornings, with DH and I sharing the tuition and practicing in the afternoons.
The Tuesday was the first day we ventured off the nursery slope. I cannot tell you how many times DH and I fell over. I remember texting my friend some photos that evening, whilst laid on the sofa with muscles I didn't know I had aching, and she asked if we'd completely fallen in love with it. I replied that I didn't know and that today had been HARD!
The next morning, I went down the first 'big' blue that I'd gone on with my instructor the day before, but this time on my own as DH had opted to have a rest morning and our lessons had finished. I made it from the top to the bottom of that blue without falling over once. Just taking my time and snowplough turning. I cried when I got to the bottom. I was so proud of myself.
That gave me such a boost, and my love of skiing was born.
My advice would be to practice repeatedly on a run you're comfortable on to build confidence and take lots of tea and cake breaks.
I wasn't parallel by the end of that first week, not even close, so that won't come this week, I'm afraid. But you should absolutely be able to control your speed in other ways by the end of the week. Forget parallel. Absolutely nothing wrong with snowplough turns whilst you build confidence to keep you safe and get you down in one piece. Parallel will come later.