Long Lines of Litigants

Introduction

Shemot 18:13 describes Moshe's workload on the day after Yitro's arrival: "And it happened on the next day, that Moshe sat to judge the people and Moshe sat to judge the people; and the people stood about Moshe from the morning to the evening." Was this a one-time aberration or was there always a never ending line of people coming to seek Moshe's advice and wisdom?

Additionally, the Torah specifies that this happened "on the next day." From this one might conclude that there was not a similar problem on the day on which Yitro came. But if so, why not?