SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'a12851641291432b3a91fc1a319d1f8f283ba69dc9ff5c254b3266baad0f7a51' 
  AND token = 'ZJ4G6YOwmVPCcPJgeduRlkRzcImnMW/SRyQRKw+Gatk=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00027

JSON explain

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