SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'b1248903c4068b891ef911f38f2868041f9cba1cd0c4d6c6a9cc75853ae3f421' 
  AND token = 'c+nNeRtDIFxFuMUrSQrTUQsVcXnGq5i1tUj0V3eMXEM=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00031

JSON explain

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