Greetings,
I would like to thank you Serhii Pustovit for sharing script.
Please find the finale script along with screenshot that worked in ISE 2.1-P6
Requirement-1
On sponsor portal when we fill out Access Information for guest accounts, the system auto-populates an ending time of 23:59; to set ending time be 18:59 or any custom ending time,

We need to go to portal page customization on sponsor portal and then go to sponsor portal settings and under "Instruction Text" click on "Toggle HTML source" and paste the below script
<script>
setTimeout(function() {
$('.dateTimeGrid tr:nth-child(2) .colRight input').val('18:59');
}, 2000);
$("#availableGuestTypes").on('click', function(evt) {
setTimeout(function(){
$('.dateTimeGrid tr:nth-child(2) .colRight input').val('18:59');
}, 3000);
});
$("a.ui_create_accounts_button").on('click', function(evt) {
setTimeout(function(){
$('.dateTimeGrid tr:nth-child(2) .colRight input').val('18:59');
}, 3000);
});
$('#createKnownAccountsSummary [href="#page-create"]:last').on('click', function(){
setTimeout(function(){
$('.dateTimeGrid tr:nth-child(2) .colRight input').val('18:59');
}, 1000);
});
</script>
Here is screenshot

Once this script is saved, if we login to sponsor portal and try to create any guest account, an ending time will show from
23:59 to 18:59

Requirement-2
For Guest Type: "Maximum devices that can be connected:5 | Maximum access duration: 5 days" we would like to change the color so that it is more visible

We need to go to portal page customization on sponsor portal and then go to sponsor portal settings and under "Instruction Text" click on "Toggle HTML source" and paste the below script
<style>
body .guest-type-description {
color: red;
}
</style>
