The difference between 立刻 and 顿时

A classmate whatsapped the group asking, what's the difference between 立刻 and 顿时?

You know what - I dunno, so I googled.


立刻
EN: right away; immediately
CN: 表示紧接着某个时候，马上
Sentence1: 请同学们立刻回到教室去。
Sentence2: 老师一进来，教室里立刻安静了。

顿时
EN: suddenly; at once
CN: 很快地；一下子
Sentence1: 听到这个好消息，各种欢呼声顿时在全程响起。
Sentence2: 她看到他非常高兴，顿时完全忘记了之前的烦恼。

"两者都有在很短的时间内动作很快地开始或结束的意思，但是顿时只用于描述过去发生的事情，立刻咩有此限度，顿时不能用于祈使句，立刻可以。"


Hmmm. So the biggest difference is in "suddenly" vs "immediately".

Another person within the group replied with an answer that I think is so much better that the above: 立刻通常指马上去执行一个行动。顿时是指一个时间点，像突然间。eg: 顿时恍然大悟。

So nice to have such awesome classmates.