As a general rule an animated video for marketing purposes will most likely not be more than 2 minutes long with the average length about 1 minute. There are two reasons for this. 

1. Most animated explainer videos are going to be used with your online marketing therefore it is most likely going to be used as as promotional content. Thant being said the video needs to be short and to the point. 

2. You need to keep peoples attention. It's been said that we have less attention while viewing content on the Internet than a gold fish. So you need to grab the viewers attention right away and keep their attention with fun, entertaining and informative content. 

One minute of content is going to require a script of around 140 -145 spoken words. This is actually great news for those who have a hard time coming up with what it is exactly to say. 

Just hit the who, what, why, where and how and you should be good to go. Remember to always have a call to action at the end of your video and perhaps throughout the video by having a website address right at the bottom of the video the entire length of the animated video. 

Some videos posted on Instagram or other platforms such as YouTube shorts should definitely not be longer than 1 minute as the formate really wants shorter videos, hence the name YouTune shorts.