SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'b6d94b6015509119538679a41e4533c80c2e0b00b21726529af15f9966138707' 
  AND token = 'oEiJNQOlmug5p+0UOSqi3FmuVdAPvQD2qF7UXjZsvg0=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00025

JSON explain

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