Reading the FBI data in.

gistfile1.r

df <- read.csv("data.csv",
                 header = T,
                 stringsAsFactors = F)

df$date_put_on_list <- as.POSIXct(df$date_put_on_list, format = "%m/%d/%Y", tz = "EST")
df$follow_up_date <- as.POSIXct(df$follow_up_date, format = "%m/%d/%Y", tz = "EST")
df$days_to_capture <- ifelse(is.na(df$follow_up_date) | df$follow_up_date == "",
                            difftime(Sys.time(), df$date_put_on_list, units = "days"),
                            difftime(df$follow_up_date, df$date_put_on_list, units = "days"))
df$censor <- ifelse(!is.na(df$follow_up_date), 1, 0)
mean(df$days_to_capture[df$days_to_capture > 0 & df$censor == 1], na.rm = T)

[1] 402.2239 # days