SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '78eca4c6aeb72a1c14023c6d15530adfd19a59858fd19a60408a3093d7f4f358' 
  AND token = 'PluWHJevZ7bJ0bUItPNub5EvIvbsngnHDkhLQuKxwpI=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00033

JSON explain

{
  "query_block": {
    "select_id": 1,
    "message": "no matching row in const table"
  }
}