Time for someone to declare their new holding. How long does a...

Time for someone to declare their new holding. How long does a company or individual have before they are obliged to declare they have become a significant shareholder or increased their stake? One time it took JP Morgan months to declare they had disposed of shares and likewise months to declare they had bought in again. In the meantime other shareholders are left in the dark. This could be an attempted takeover by stealth. It would seem likely that a single shareholder has bought the bulk of the JPMorgan shares.
We need to bear in mind that they cannot gain 51% without those shares held by the Carr family and the second largest shareholder. They'll need to negotiate. Certainly they can buy a few million at around 50-52c but the rest should surely cost a lot more. Their average will be marginally better than than with a full-frontal takeover offer.
Management have access to the share register and in theory we all do, so we could find out. I wouldn't want to bother Elaine at a time like this though.
I did buy a small parcel at 50c yesterday as a top up. It does seem that this is the real bottom price right now.