I want to ask about an effort that we are doing in a city in Romania, we collect on Saturday and we go to visit people's homes and we go in the streets and give da'wah to Muslims at 7o' clock. But the time varies and even the day varies, or can be other day. We go to people at other times also. Is this Bida'h?

Praise be to Allah, the Lord of the Worlds; and blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.
If the day and time could be changed regarding the circumstances and if you do not stick to a given day or a given time, there is no harm in that and it is not an innovation. We ask Allah to grant you success in what pleases Him. It is likable to change the day and date whenever necessary.
Allah knows best.