We aim to study the time evolution of the SiO maser lines in Mira-type and semi-regular variables at short timescales. We observed the SiO maser lines at 7mm and 3mm using the 40m Yebes antenna and the 30m IRAM telescope, respectively, with a minimum spacing of 1 day. We studied the semi-regular variables RX Boo and RT Vir and the Mira-type variables U Her, R LMi, R Leo, and chi Cyg.