SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '6e321d1170197822ab2b27991bb5c4cce756ead7fc40e70697c515c32e700016' 
  AND token = 'sCVmLWhoVsuTDOsEiYhDphNOIHy2buVkRrvutahKA3k=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00031

JSON explain

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