No Time To Waste

Someone once asked  Harav Elyashiv zt"l:

At Nichum Aveilim when should one say

the Hamokom Yenachem Eschem- at the start or  at the end of the visit?

Rav Elyashiv responded he didn't understand

the question. 

"You are supposed to walk in say Hamakom- and leave"

שמעתי מהרב י' ט ייכמן ש ליט"א המקום ינחם אותו וב"ב

What Is The Mekor To Saying Hamokom Yinachem By A Shiva

The Minhag for Ashkenazim, when being Menachem Aveilim, is to say:

 “ Hamakom Yenachem Eschem B’toch Shaar Aveilei Tzion V’yerushalayim”

 Some Aveilim have this text hanging behind them, so that the Menachmim will know to say the exact Nusach. 
 This text does not exists in Bavli, Yerushalmi, Rambam, Tur or Shulchan Aruch. 

 The first source of this Nusach, is in Shu”t Shvus Yaakov (3 : 98) He writes if one of the Aveilim is Menachem other Aveilim he should say Hamakom Yenachem Eschem VEOSONU