You absolutely have to pursue Chris Ash until he tells you no. He would be a home run hire and has strong ties to BIelema. Texas letting Herman go could be a huge benefit to get a DC with Ash's pedigree.
You're correct it was originally slated to start 3/11. On Saturday there was an announcement that Spring practices wouldn't be starting until head coach and staff were in place. Today Lovie did mention no later than beginning of April. So best guess is late March, beginning of April.