Do you need to go to the ER if you can't urinate for a few hours?

My dad went to the Emergency room right away just because he didn't or couldn't urinate and he didn't even wait, he waited like 2 hours. I feel like he does not need to go for this unless it's been longer than that. My dad is 61 yrs old and he has gone to the ER before for this same reason when he didn't even wait. He went when he was 58-59 yrs old. My neighbor who is much older than him, he's like 90yrs old and he didn't go until he waited 1-2 days. I think his condition could wait a little longer, and he does not see his regular doctor either. This is not a life threatening emergency unless it's been longer than that. I think going to the ER may even make things worse because he started to bleed after they used a catheter. He did not bleed before and had no pain either, maybe some mild cramping from not urinating.