RTC program with led lights for aquarium

Hello everyone.

My question may sound stupid, but I am pretty new on arduino logic and I would like to understand a bit better.

I've wired up an rtc module with my Arduino Uno and uploaded a sketch that set's up the clock. As soon as i did this a led light started to blink in a systematic way, reminding the frequency of a clock.

Ok. After that I uploaded another sketch that will control a led light string, turning on and off after a specific time, using PWM.

I have not tested yet, but as soon as I uploaded the led sketch (let's call it that way) the led light from the arduino stopped to blink and I cannot see anymore the time and date from the serial monitor.

My question is... after i uploaded the new sketch will my arduino keep the time correct? Will this new sketch be able to work with the time logic? Why cannot see it from the serial monitor anymore? Ps.: I have researched the internet trying to understand this, but seemed to be so basic that it dosen't have so much material.

best regard