UpdateProjectBuildSchedule.ps1

$env:API_TOKEN = "<replace>" # from https://ci.appveyor.com/api-token
$env:APPVEYOR_ACCOUNT_NAME = "<replace>" # from AppVeyor project URL
$env:APPVEYOR_PROJECT_SLUG = "<replace>"  # from AppVeyor project URL
$env:CRONTAB_EXPRESSION = "<replace>" # e.g. "5 * * * *"

$headers = @{
  "Authorization" = "Bearer $env:API_TOKEN"
  "Content-type" = "application/json"
}

$s = Invoke-RestMethod -Uri "https://ci.appveyor.com/api/projects/$env:APPVEYOR_ACCOUNT_NAME/$env:APPVEYOR_PROJECT_SLUG/settings" -Headers $headers  -Method Get
$s.settings.scheduleCrontabExpression = $env:CRONTAB_EXPRESSION 
Invoke-RestMethod -Uri 'https://ci.appveyor.com/api/projects' -Headers $headers  -Body ($s.settings | ConvertTo-Json -Depth 10) -Method Put