How to add $hash variable in webasyst?

Question

CMS

Hello.
I work with webasyst in shop-script.
How can I add another condition to a variable? And what does %2000:00:00%26 and %2023:59:59%26 mean?

$hash = 'search/update_datetime>='.$update_datetime_from.'%2000:00:00%26update_datetime<='.$update_datetime_before.'%2023:59:59%26state_id=completed';