Kept at room temperature, a starter ideally shouldn't go for more than a couple of days without feeding, or it will lose activity. Too much longer, and it could start to die out, possibly inviting mould. If you refrigerate the starter, a weekly feeding is ideal, but if absolutely necessary it will likely survive well for a couple of months before activity is significantly lost. Should you "kill" a starter and it ceases most or all activity, however, the good news is that 1 or 2 feedings will usually revive it! (In the latter case, move to a clean container for food safety).