get baby to nursery for 730, I am then off to work by 745, get there just before 830, and pick baby up around 4. It just seems really easy when I put it like that but DH has so many what ifs
The first thing to decide is whether you want to be a SAHM. Some do, some don't. Your situation sounds as if you genuinely have a choice, so it is important for you to work out what you want.
Your plan sounds as if it will work fine when all is going to plan. The thing about plans though is that we know that it doesn't always happen like that.
I'm certainly not a worrier but I do think it is important to calmly consider what might go wrong and know what you would do in that event. I know I don't make very good decisions when I am under pressure so I would know what my plan wad in the case of illness, mine, DH's, the baby. Then if it happens you just do what you had decided and agreed when everything was calm.
baby was unwell during the day you just say ‘I’m sorry, I will have to go and pick my baby up, he is ill!’
While this too is absolutely right, won't it depend on how often this situation arises?
As a one off or even annual event, I'm sure that everyone would accommodate you. How will it work if your baby has a run of illnesses? Right when you are at a crucial stage at work. Obviously it will depend on your role: we you aren't contribution they you don't get the credit for new initiatives. Your role might even become a little vulnerable.
What plans can you have in place for this situation?
If you do decide to become a SAHP then do make sure that financials are absolutely fair between you, you have have your own savings and pension etc. in your own name. That you also get some time and space to yourself and opportunity to get ready to rejoin the workforce.
There are no really wrong answers, good and bad things about whatever you do. The only mistake is to slide into being a SAHP without think (and talking) through all the scenarios and potential impacts. Not to be afraid, but to be ready, as a team, for whatever comes.
In your shoes, I'd apply for any job I fancies regardless. Plenty of time to decide what to do once you have been offered the job. No applying incase you get it will reduce your options considerably.
Good luck