Usually OnTime® Mobile is delivered to the whole organisation from a central place, this would usually be through Mobile Device Management Solutions, and therefore it shouldn’t be up to the user to do this manually.
In order to make an OnTime Mobile Web App in iOS, you have to open your mobile client in safari, using the link you would usually use to open the Desktop Client online, but replacing the word desktop with mobile. You can then click on the square icon with an arrow pointing upwards in the middle of the bottom panel. In the lower part of the box that opens, you can then choose “Add to Home Screen”. You can name the Web App e.g. OnTime Mobile, and click add. You will now have easy access to your OnTime Mobile Client from you home screen.