May I use a blech with a timer on Shabbos? Is taking a pot off the blech Erev Shabbos and heating it up on the next day for Kiddush with the set timer permitted? (The food is fully cooked and intended to be put back).

ב"ה Shalom It has become accepted to use the Shabbat timer for an electric "blech"=food warmer= "platter " to warm food on Shabbat. However, as you specified the food must be fully cooked. In addition, when placing the food there on Shabbat, according to Shemirat Shabbat Kehilchata (1:30) it should not be placed directly on the platter ,but there should be something between the pot and the blech, even if fully cooked. However, there are those who are more lenient to place it directly on the blech when fully cooked without separation, since the food warmer is not meant for cooking and therefore, we need not worry about the concern that it looks like cooking. ( (יחווה דעת ב:מה,ציץ אליעזר ח:כו והביא שכך גם פסק רב צבי פסח פרנק זצ"ל All the best