想要操纵日期命令来计算今天以后的未来

I have this snip of code I have been using in an alarm script I hacked together and have been using with success for the last year or so. But it has always been limited in the sense that if I specify an alarm duration that would extend beyond midnight, past 23:59, then the alarm simply sounds off immediately.I have this snip of code I have been using in a