They actually do have to articulate their PC. If they don't, again, you can sue for civil rights violations. Not saying it doesn't happen, it does, but it's not correct to say they're "allowed to".

They have 24 hours to articulate that or let you go.

They still have to explain why you have been detained, right?

From my experience having been arrested and held like this before: No. They don't even have to attest to probable cause until the 24-hr limit hits, in which case they will then formally arrest you by taking you to be fingerprinted, a reading of Miranda, etc along with paperwork containing the attestation of probable cause, or let you go, again, with a pile of paperwork, and sometimes both, in which case they arrest you formally, give you paperwork, and an issued summons to appear in court before sending you on your way.

No

Burden of proof is different for detaining, arrest and when in court if one is charged.

They have to have PC to arrest someone. Even if you're not charged, PC has to be there for an arrest to be justified.

They can detain you briefly for something as simple as wearing jeans if someone committed a crime while wearing jeans but typically this is only for a handful of minutes. These reporters were fully arrested which is a different standard as you've written already.