// start of day in date (2021-01-01 00:00:00)
Carbon::now()->startOfDay()
 
// start of day in timestamp (1609459200)
Carbon::now()->startOfDay()->timestamp
 
// end of day in date (2021-01-01 23:59:59)
Carbon::now()->endOfDay()
 
// end of day in timestamp (1609545599)
Carbon::now()->endOfDay()->timestamp