I have remained active all day on MF, but WSPRnet only shows stations spotted in the last 10 minutes, so if there is no-one else spotting you, you do not get shown as being active. This is a pity, as it does not encourage people to take a look. Instead they may look elsewhere. I don't know why there is this 10 minute rule, but personally I find it unhelpful. It would be better to show all stations active, whether or not they are being reported.
UPDATE 1845z: G4AYT (114km) has been copying me weakly, but consistently, for some time. He is located on the North Kent coast (JO01mi).
UPDATE 2022z: M0PPP (182km), in IO93gm square, has been spotted here consistently this evening on my earth-electrode "antenna" and deaf FT817 RX on 472kHz WSPR.
UPDATE 2145z: PA0RDT (243km) is now spotting me.