SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '51c8180c043f8afbf080867273f765c665728c5f378daabaf9286514c5fb5f37' 
  AND token = 'DS4Yc0bjQLzU63g4AjcgwpWvt/8KgBBEVkdWjFU04rg=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00011

Explain
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE Impossible WHERE noticed after reading const tables