SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '255bc57f5dfa4222563abd2a602a761f0903d69875413c8009a56bebc7a6ccd8' 
  AND token = '/QXJ3PWvqbrKUBCFYWMzOilDBca+tgRO/+TiC5ls/Mc=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00019

JSON explain

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