This is someone I've known for a long time but we were both single for the first time and we went on a date the date was a little awkward. He wants to keep it casual but how long should I give him to get in contact with me before I deem it a lost cause
Never assume any date to be a lost cause , that is unfair to the both of you. Back in my dating days I made this mistake with a girl I went out with. If your in question call/ message him. You said it was awkward , if he is embarrassed about it for some reason he may hesitate to make contact but that doesn't mean he isn't interested
to answer your title question, I text the next day.
to answer your details/situation, I'd say text him after a few days if he doesn't text you. tho if he doesn't text you, it's probably b/c he isn't interested. or could just be embarrassed from however awkward it was.