How to code multiple conditions inside if statement?

I'm not sure how quickly you soil could get dry, but I suspect what you want to do is to periodically check the dryness throughout the day. Say like every two hours:

// Check every 2 hrs (when hr is even)
if ( t.hour % 2 == 0 && moistureOneSensorValue >= 700 ) {...}

You could also bound it to only during the day time:

if ( t.hour >= 7 // after 7a
  && t.hour <= 19 // before 7p
  && t.hour % 2 == 1 // every 2 hrs (when hr is odd)
  && moistureOneSensorValue >= 700 // soil is dry
) {...}

If the event is to be time independent then it follows you can not check the time. If the event is to be both time independent and dependent then you need to add the code to handle the logic.

Consider checking if it is between 7am and, say, 7pm. If true then test if the moisture detector is dry. If true then close (watering) relays.

(This is only a code example and has not been tested.)

if(t.hour >= 7 && t.hour <= 19)
{
  while(moistureOneSensorValue >= 700) 
  {
   RelayOne();
   RelayTwo();
  } 
}

Consider adding a state machine to mitigate possible problems by monitoring minimum times between events and maximum times of events. For example, do not water more than once per 5 minutes. Do not water more than 30 seconds at a time. Do not water more then a total of 1 minute per hour. Do not water more than 5 minutes per 24 hours.