The default format for the countdown time is HH[h]:mm[m]:ss[s]

HH is the hour
mm is the minutes
ss is the seconds
[h] is the letter h appended to hours
[m] is the letter m appended to minutes
[s] is the letter s appended to seconds

For example, you can change the format to HH[hours]:mm[minutes]:ss[seconds] which will output:

We are opening in 03hours:56minutes:01seconds. Please check back later. 

You can also remove seconds if you dont want to show seconds HH[hours]:mm[minutes]

which will output:

We are opening in 03hours:56minutes. Please check back later. 

Please visit this link for list of time format cheatsheet: https://help.mywpdev.com/article/time-format-cheatsheet/