For function.json I had the following

{
  "bindings": [
    {
      "name": "Timer",
      "type": "timerTrigger",
      "direction": "in",
      "schedule": "0 0 8 * * 2-7"
    }
  ]
}

Changing the days of the week to their Names fixed the issue

{
  "bindings": [
    {
      "name": "Timer",
      "type": "timerTrigger",
      "direction": "in",
      "schedule": "0 0 8 * * Tues-Sun"
    }
  ]
}