URGENT: Last Dialogue Time import not recorded, fields remain blank

URGENT: Last Dialogue Time import not recorded, fields remain blank

I'm trying to import last dialogue times for ~2000 prospects. I have followed the exact date/time format as indicated in the import section and have even tried different formats. Nothing works. This is very frustrating as our ~2000 key prospects now lack lack Last Dialogue Times and this has messed up all our reminders.

Can someone please help me out? I've already tried called you, livechat and the customer support section. Nothing so far, this is very frustrating!