First, remove the colon before Informat(). That is telling JMP that Informat is a column name. Start by taking those colons out. You can also simplify your script like so:
sel rows = sdt << Get Rows Where(Informat("06/26/2018 16:49:00", "m/d/y h:m:s") <= :Time <= Informat("06/26/2018 16:54:00", "m/d/y h:m:s"));
sdt:Status[selRows]="2";
You also need to verify that Status is character column. If it's numeric (even if the modeling type is nominal or ordinal), you need to remove the quotes around "2".
-- Cameron Willden