SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'c879cbaa54343e60df1298a1a165db3e8578c0f90e8519bb9dc4b3f36e3556e3' 
  AND token = 'UoSILrufKYTb/enxrZmlPQzUEggCwTRwcpgydRu+VAc=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

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