How to make Firebase Api for the scheduled notification usin

I am creating an application in that I need to implement scheduled push notification in an application. Currently, I am sending notification currently and that is working fine. Now I need to use API for sending a scheduled notification.

I try with below code for scheduled notification:

var obj = new
{
to = Id,
data = new
{
title = Title,
text = Message,
icon = Icon,
schedule = new
{
startTime = new
{
date = new
{
day = 19,
month = 8,
year = 2019
},
time = new
{
hours = 11,
minutes = 07,
},
timeZone = "Asia/Calcutta"
},
}
},
};

Through the above code, notification is sent but not as per a particular time period.

Can anyone look into this and suggest me what should I have to do in that?