Wow. TO for an infant. I actually think that's cruel; I hope that you are able to resolve that with the daycare if they are using that to punish you dc. I cannot even imagine doing that. In our experience, with highly verbal, early talkers, TO there would have begun for ds1 and ds3 at four months and for ds2 at 2 months. Children develop at different intervals and if you're not there with them, helping them to manage whatever is overwhelming them, they are being left alone to cope without adequate coping skills; their age doesn't really matter. Goodness, I still have the occassional meltdown and having someone to talk to who cares for me and isn't just going to walk out on me is so much more valuable and actually empowering and reassuring! It's funny, a good kennel wouldn't do that to a crying puppy...
Anyway, I think that tantrums are normal whenever they happen. If I had relied upon milestone charts to tell me when tantrums were 'appropriate,' I would have completely missed out on a years of our dc's lives during which time they obviously really needed me.
I'm not saying it's a waste of time to be aware of common age-related stages and 'normal' behaviour, just that in the end, it's just you being there for and with your child, whether or not he/she conforms to the norm. I suspect most children don't fall within the 'norm' at some point (or every point...).
I personally wouldn't ever ignore a tantrum. I try to help them identify what they are feeling by speaking to them through it, offering hugs & kisses, reassuring them that when they are ready, I am looking forward to hugging them, talking, helping, telling them repeatedly that I am staying with them, and I NEVER leave. It used to be stressful, but now I relax knowing that I don't have to control the situation or fix it at all. I just have to be there and be willing to help them work out their issue. I do sometimes have to move them so hey don't hurt themselves, but I don't place restrictions on how they are allowed to behave during a meltdown. Our almost four-yr-old doesn't have tantrums anymore, ds2 does rarely, and ds1 does about once or twice/month or less. I try very hard to head off a meltdown by talking to them when i see them boiling up. Non-violent-communication has been key to a near-eradication of meltdowns, I think. It's funny though, NVC was just natural with dc when they were freaking out or about to as infants, but with older children, it seems to take a conscientious effort (for me).
I should also mention that our dc are not mild or compliant in temperment. They are very intense, very strong-willed, spirited and different in personality from one another and dh and I. It's pretty amazing that we all live together, actually. What we all have in common seems to be an unrelenting intensity and drive in every way. We're exhausting, if I do say so myself!

Also, this is what it is like right now. I make no claims that how things are now will continue because our home is always in flux in some way or another and I might be posting about how to deal with my dc's tantrums six months from now. I don't know, but I'm open to being there and in the moment with them, so we'll figure it out somehow, together.
I hope that you can find peace in this with your family, sincerely. I know it can be stressful. It can also contain a seed of liberation if you want to and can find it.

ETA: I think imposed TO for any child is cruel actually. Ds1 sometimes takes his own without prompting; that's fine, his choice and a mature decision, I think. I take TO's too, but
pushing away someone who's hurting at any age cannot possibly be the solution to their pain or restorative to the relationship. I just can't see it.