@EveningSpread is spot on.
@LeeJames1, you claim to be a specialist and to know all about attachment theory but some of your posts really don't reflect that. It comes across as although you've decided on a nursery place 2 days a week, you're already shooting the idea down and looking for reasons why it won't work.
Two days a week in nursery will not harm his secure attachment. I would have thought you'd know this.
Separation anxiety is at a peak around 12 months so it's likely to take longer for a child to settle.
A good quality childcare setting is not 'less than ideal.' It can provide an excellent addition to the primary care given by parents. It's not a replacement or an alternative, it's an addition alongside the care and stimulation and experiences at home.
When you're in the middle of it, returning to work and settling them into childcare, it can be difficult to separate the reality from the emotions.
When you're able to look at it all more objectively, you'll know that what you're doing is normal and absolutely fine. My 3 children are all happy, successful well adjusted adults. Living proof that good quality care is not damaging!