What is the best way to gradually increase the value?

Question

PHP

Let's say we have regular php and mysql
. Population value is 100 people. The happiness parameter was 0, they built a monument to Lenin, it became 20
Question: how best to gradually increase the happiness of the population from 0 to 20?
The idea that came up right away is to bypass the crown every minute and look, for example
if(current happiness < maximum happiness) { increase the current one by 1 }
And so on until the current one becomes 20. But if there are a lot of users in the database and everyone has such a parameter or several, is this method rational?
PS There are other solutions when the parameter increases non-linearly, but there are no special ideas here, for example:
0-5 - 3 units. per hour
5-10 - 2 units. per hour
10-15 - 1 unit. per hour
15-20 -0.5 units at one o'clock

Answer 1

set the timestamp after building the monument.
when someone asks for a specific value, plus it depending on the timestamp,
respectively, this requires that the game object is not just a set of parameters, but also has the logic of work in the form of functions that "smartly" get and set values