Generally, you can create a program and set it to ‘disabled’ (i.e. enabled flag is off). This way it doesn’t matter how you program its day / time, the program won’t run normally, but it’s available to be triggered using buttons or sensor input as switch. To use buttons, you can press and hold button B3, to activate the ‘manual run’ program feature, there you can select any program (including those that are disabled) to run. To use sensor input (which you already know): the second sensor can trigger the second program. Again, if you set that program to disabled, then it won’t run normally, so you can set any day / time as you want.