public Builder mergeStartTime(com.google.type.TimeOfDay value) {
      if (startTimeBuilder_ == null) {
        if (((bitField0_ & 0x00000002) != 0)
            && startTime_ != null
            && startTime_ != com.google.type.TimeOfDay.getDefaultInstance()) {
          getStartTimeBuilder().mergeFrom(value);
        } else {
          startTime_ = value;
        }
      } else {
        startTimeBuilder_.mergeFrom(value);
      }
      if (startTime_ != null) {
        bitField0_ |= 0x00000002;
        onChanged();
      }
      return this;
    }
<pre>
Optional. Start time of the window in UTC.
</pre>

<code>.google.type.TimeOfDay start_time = 2 [(.google.api.field_behavior) = OPTIONAL];</code>
java-valkey/proto-google-cloud-valkey-v1/src/main/java/com/google/cloud/memorystore/v1/WeeklyMaintenanceWindow.java