Arghhh how to change current plans without causing an argument?

[LalalalalaLand]

Hello, think I know what I need to do but not sure exactly HOW to do it. Apologies for the long post.

When I was pregnant with DS my DM very kindly (but rather forcefully) asked/said she would like to look after him when I went back to work part time. Since he's been here it's all she has talked about - in fact it's all she talked about before he was here too. I put up with it, even though I found it quite difficult to bite my tongue when I'd just given birth, as myself and DH are both very grateful and we realise how much money it is saving us.
About 4 weeks ago my days at work got agreed - I had no control over these days. They were given to me and it was a take it or come back full time situation.
Now DM is starting to move the goal posts quite a bit. She still wants to do some of the things she did on these days (completely fine by me, I just wish I'd known earlier) which will mean she will not be able to have him first thing in the morning and I will need to drop DS to another family members house. This will add another half an hour to an already 45 minute journey in the morning and will mean us leaving the house at 6.30am.
I wish we had thought more about it when it was first suggested. If we had chosen nursery we could have chosen one near to our house and DS could have been dropped at 8.15 by DH and picked up by me at 6, with the current plans I will need to leave with DS at 6.30am and we will not get back until 6.15pm. He will also be in the car for quite long journeys twice a day and I'm dreading the one coming home as I just know he will fall asleep and it will cause a huge issue with bedtime.

So, lovely people , how do I tell my lovely (but very forceful DM that we will need to see how it goes for a few weeks OR that we have had a really long think and just don't think it is going to suit DS, me or her.

Get the nursery place first. They often have waiting lists. When you have a place then you tell her.

Just tell her you have been recommended a fab nursery so you've decided to trial it out. .. Explain it's a bit early to be dragging a baby out his cot to get sorted before work if she had him but thanks for the offer!!

How about a child minder then she could do holiday/sick cover...

Get the nursery place sorted first.

Then say to your mum that you've been looking at the logistics for when you go back to work, and while you think it's really kind for her to offer to have DS, the timings just won't work for you so you've booked a nursery place. It'll be too stressful in the mornings etc, make it clear you have already paid for nursery so that's happening, that you just want life to be as easy as possible.

Look at child-minders and nurseries to see if anything is available before shooting yourself in the foot.
See if you can work out a compromise with her maybe doing one day and explain the hours are too much for you to cope with and too long in the car for LO.

Why don't you send him to nursery for half days ? And your dm pick him up from there? That way it's a win win. No earlier mornings and your dm still gets to see him? I think nursery is a long day for small ones though. So I'm all for family support/ home environments.

No it's too unsettling for a baby to be hauled out of the house at 6.30 and be passed between different family members during the day. Book DS into nursery for the days that DM has other activities. The hassle is not worth the money saved.