I made another char which is a trader concentrating in alchemy and something, I rushed at mining camps to get boots and ores because my friends tell me enemies respawn, I check now and then if the mines do respawn but they don't. Is it true timer resets when I revisit? Why is there no camp timers in world map nor a notificationon how does this work?

It takes 10 to 30 days for things to respawn. Look on UESP wiki. That will tell which ones respawn,which ones don't,and how many days you need to wait. If you go back in before the 10 or 30 day period it will reset to zero.

Things in the open world are usually 10 days. But some indoor areas are 10 and 30. I actually wait 11 and 31 days to be sure though. Not all places respawn either. But as i said,you can check on UESP wiki.

The dungeons should respawn Bethesda did fix dungeon respawns with 1.6 but there is a respawn bug where enemies in the wild at spawn locations and random encounters that will not respawn. It should also be noted that plant respawns are also broken and will not respawn.