SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'd21761861227d2d1c28211d97c505eb4dfa5b62f5921e742f70373e39d98dddf' 
  AND token = 'VwwwHFehz3Fr2rSMCbiKrQUqSLUY4WZs9i+mjrYzopc=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00024

JSON explain

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