I was at work with a co-worker that said back in the 70's, he believed, that it was illegal for any FBI, Police, Etc..., to listen to any phone conversation for longer than 90 seconds.

Is he correct and, if he is, does this still apply today?

Also, how in the heck is this supposed to be the law when they were planting 24-7 recording devices in certain places?

I believe that up until this present day, you must have a court order to even be allowed to listen into anyone's private conversations.

Any info on this topic is appreciated.

called minumizing. but only for non targets..kids , ect

They are good for 30 days. They then have to request another wiretap.
Back in the 70’s, they would illegally( sometimes) tap into phones or bug cars to gather info,, thats no really done today.
Pen registers were another big thing.

Always thought it was funny that gottis best friend angelo r had the phone company install a line in his daughters room. He thought that way the line wouldnt be tappd. Or was it in casino joe pescis wifes talking to someother guys wife then the swap the phone after like 30seconds. Nowadays the feds can turn you cell phones speaker part to record you talking outloud. Comes back to this bonanno guy who recorded his own induction ceromony in 2015. The genovese made there guys strip naked probaly drop n cough th en gave them a bathrobe. But they left all there belonging phones keys wallet ect at the bar back in 2003.