GET Search Service Application
$ssa = Get-SPEnterpriseSearchServiceApplication

#Get the Crawl Content Source
$cs = Get-SPEnterpriseSearchCrawlContentSource -SearchApplication $ssa -Identity "Local SharePoint sites"

#Enable Continuous Crawls
Set-SPEnterpriseSearchCrawlContentSource -Identity $cs -EnableContinuousCrawls $True

#Set the crawl interval to 10 minutes
$ssa.SetProperty("ContinuousCrawlInterval", 10)
$ssa.Update()

$ssa = Get-SPEnterpriseSearchServiceApplication

Get-SPEnterpriseSearchCrawlContentSource -Identity 'Local SharePoint Sites' -SearchApplication $ssa | Format-List -Property *

CrawlState               : Idle
CrawlCompleted           : 5/17/2018 3:53:48 PM
CrawlStarted             : 5/17/2018 3:06:28 PM
SharePointCrawlBehavior  : CrawlVirtualServers
EnableContinuousCrawls   : True
FollowDirectories        : False
Type                     : SharePoint
DeleteCount              : 299
ErrorCount               : 15508
LevelHighErrorCount      : 0
SuccessCount             : 35373
WarningCount             : 1138
Parent                   : {Local SharePoint sites}
StartAddresses           : {https://<servername>/}
Id                       : 1
Tag                      :
Name                     : Local SharePoint sites
FullCrawlSchedule        :
IncrementalCrawlSchedule : Microsoft.Office.Server.Search.Administration.DailySchedule
CrawlStatus              : Idle
ContinuousCrawlStatus    : Crawling
CrawlPriority            : Normal
RefreshCrawls            : Enabled