user cannot submit the form

What is the use case for this? Also, do you only have Nintex Forms or also Nintex Workflow available to you?

In nintex form, user is filling the data and saving to the list. so, there are some approvals to happen in that 24 hours, so user should not submit the form in that 24hours from the time of submission.

Are you using workflow?

based on what you've said here, it seems like your requirement is that the user should not be able to resubmit prior to approvals / rejections - not just "for 24 hours."

in which case i'd suggest using a workflow - once the item is submitted, lock it down for only the admin (or whoever is doing approvals), and unlock it once approved. You could even hide the submit button to the initiator, or hide an entire panel, or remove their permissions entirely. Lots of options. 

It will go for approval, but user needs the validation in the form itself so that 2nd time if user tries to submit it should not get submitted

You could use javascript to check a list item exists for that user.

First I had to get SPServices for jQuery.

NWF$ | The Chris Kent 

Then I added custom javascript to the form.

function check_for_recent_form(ListName) {
    var today = new Date();
    var diffMs = 0;
    var diffNarr = "";

    NWF$().SPServices({
        operation: "GetListItems",
        async: false,
        listName: ListName,
        CAMLViewFields: "<ViewFields><FieldRef Name='Created' /></ViewFields>",
        CAMLRowLimit: 1,
        CAMLQuery: "<Query><Where><And><Eq><FieldRef Name='Author' /><Value Type='User'><UserID /></Value></Eq><Geq><FieldRef Name='Created' /><Value IncludeTimeValue='TRUE' Type='DateTime'><Today OffsetDays='-1' /></Value></Geq></And></Where><OrderBy><FieldRef Name='Created' Ascending='False' /></OrderBy></Query>",
        completefunc: function (xData, Status) {
            NWF$(xData.responseXML).SPFilterNode("z:row").each(function() {
                var LastCreated = new Date(NWF$(this).attr("ows_Created").replace(" ","T"));
                diffMs = 86400000 - Math.abs(today - LastCreated); // milliseconds between now & LastCreated
                var diffDays = Math.floor(diffMs / 86400000); // days
                var diffHrs = Math.floor((diffMs % 86400000) / 3600000); // hours
                var diffMins = Math.round(((diffMs % 86400000) % 3600000) / 60000); // minutes
                if (diffDays > 0) {
                    diffNarr = diffNarr + diffDays + " days, ";
                }
                diffNarr = diffNarr + diffHrs + " hours, " + diffMins + " minutes";
            });
        }
    });
    if (diffMs == 0) {
        return 0;
    } else {
        return diffNarr;
    }
}

I then created a form variable to call the function upon load.  The calculation of the variable would be

check_for_recent_form({Common:ListName})

You can then use your form variable on formatting rule to show/hide a message or disable other controls.  Also, the function will return the number of hours and minutes until the user needs to wait until they can submit again.