Great Thread I'm also in the boat.
You sound like a lovely mum by the way 
Maybe take the pressure off yourself in terms of a deadline? There is no right or wrong time.The timeConstraint will only make it worse. Maybe think of positive steps like me. Squirrelling away money, photocopying documents, thinking about where you would live?
In my case I have a DS age 3 and I'm pregnant with my second due to arrive soon. It certainly doesn't feel like a good time to leave. But when is? The last sobering 7-8 months during pregnancy have allowed me to think clearly and put my thoughts into perspective.
I've told my DH that once baby is here im going. He's not a very good communicator so I torture myself wondering where I'm going, how it will Pan out basically going in circles in my mind. People tell me or I read that this phase is harder than the doing phase. I haven't told too many people apart from my mum/sibling.
I play down the severity of my misery as I don't like them worrying but I've looked at renting somewhere near them before my DS starts school in September so maybe 2/3 months over summer as a trial for me/kids.
Granted I'm sure it won't be easy as I love where I live and where I'd be going I won't however I'll have support from family.
The biggest catalyst for change and pressing forward for me is my kids. I know this situation I'm in isn't going to get better. There is no physical abuse but we are both mean to each other. I send him horrible texts about how he makes me sad, lonely, (he slowly withdrew Affection, Intimacy, sex) and I've become isolated, anxious, unsure when I was a bubbly, outgoing, loving person before. Yes I blame him. But I don't want my kids witnessing our relationship as 'the norm' that's my concern.
I'm hugely emotional as a person and find it hard to hide my feelings. Weekdays are manageable when he's at work but weekends are difficult when we are together and I hate the atmosphere in our home for my DS. My DH is a great father. But he's controlling and gets annoyed when things dont go his way. So even when we are trying to be civil our DS picks up on vibe.
I think ultimately life is too short to feel like this. He has finally agreed we can't go on like this. We sleep in different bedrooms. I haven't booked any holidays for next year so try and avoid making more plans together if you're Serious about leaving. I know that's hard too. It's so hard when you're in it. I think by telling people it also means you are more likely to act on it. Something im yet to do myself (fiercely private) but take comfort in knowing you're not alone. You deserve to be happy.
I would love someone to wrap their arms around me and tell me it's al going to be ok. This pregnancy I've felt so lonely and vulnerable. Nurturing/growing another human being whilst I feel so vulnerable myself. But in a way I know I'll be okay.
Having my DH around and knowing I feel like this but him being so emotionally cold towards me despite me carrying his child is almost like what I needed to man up that if he can be like this during pregnancy what does our future hold together as a couple? We have no convention left.
Not a great deal in my eyes. He has proved himself to me during this vulnerable time and for that I'm kind of grateful as it's the catalyst for change i need.
Good luck!!! Stay strong 