The dating phase shouldnt last very long. If you are dating two people at once and you are behaving respectfully and morally with each of them, you arent cheating on anyone. First, the period of dating two people at once shouldnt last very long.

Is it cheating to date more than one person at a time?

Yes, it is cheating unless you both agreed to have an open relationship. If there was no discussion or agreement and the other person thinks they are the only one, then you are cheating.